Demerol (meperidine HCl/PF)

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Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

Meperidine/Ritonavir

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Ritonavir, a moderate CYP2B6 inducer and weak CYP3A4 inducer, may induce the metabolism of meperidine to the primary metabolite, normeperidine.(1,2)

CLINICAL EFFECTS: Concurrent use of ritonavir and meperidine may result in decreased levels of meperidine, elevated levels of normeperidine, and CNS toxicity, including seizures, profound sedation, respiratory depression, coma, and/or death.(2,3)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The manufacturer of meperidine states that concomitant use of meperidine and ritonavir should be avoided.(4) The manufacturer of ritonavir states that dosage increases and long-term use of meperidine in patients receiving ritonavir are not recommended.(2) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(5) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(6)

DISCUSSION: In a study in eight healthy subjects, the administration of a single dose of meperidine (50 mg) after 10 days of ritonavir (500 mg twice daily) resulted in decreases in the meperidine area-under-curve (AUC) and maximum concentration (Cmax) by 67% and 60%, respectively.(3) The AUC and and Cmax of normeperidine increased by 47% and 87%, respectively.(2)

Opioid Analgesics/Opioid Antagonists

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Naltrexone, nalmefene, and samidorphan are opioid antagonists and thus inhibit the effects of opioid analgesics.(1-3)

CLINICAL EFFECTS: Concurrent administration or the administration of naltrexone within 7-10 days of opioids may induce acute abstinence syndrome or exacerbate a pre-existing subclinical abstinence syndrome.(1,4) Patients taking naltrexone may not experience beneficial effects of opioid-containing medications.(4) Samidorphan can precipitate opioid withdrawal in patients who are dependent on opioids. In patients who use opioids, delay initiation of samidorphan for a minimum of 7 days after last use of short-acting opioids and 14 days after last use of long-acting opioids.(3) Concurrent use of nalmefene tablets with opioid agonists may prevent the beneficial effects of the opioid.(2)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The manufacturer of naltrexone states that the administration of naltrexone concurrently with opioids or to patients dependent on opioids is contraindicated.(1,4) Patients previously dependent on short-acting opioids should be opioid-free for a minimum of seven to ten days before beginning naltrexone therapy. Patients previously on buprenorphine or methadone may be vulnerable to withdrawal symptoms for as long as 2 weeks.(1,4) The manufacturer of naltrexone states that the naloxone challenge test, described in the naltrexone prescribing information, can be administered to determine if patients are opioid free.(1) The manufacturer of samidorphan states the concurrent use of samidorphan in patients using opioids or undergoing acute opioid withdrawal is contraindicated. Prior to initiating samidorphan, there should be at least a 7-day opioid free interval from the last use of short-acting opioids, and at least a 14-day opioid free interval from the last use of long-acting opioids.(3) The UK manufacturer of nalmefene tablets (for reduction of alcohol consumption) states the concurrent use of opioid analgesics is contraindicated.(2) Suspend the use of nalmefene tablets for 7 days prior to the anticipated use of opioids (e.g., elective surgery).(2)

DISCUSSION: A double-blind, randomized, placebo-control study evaluated pain relief and side effects of 35 opioid-naive patients undergoing cesarean section. All patients received spinal anesthesia (bupivacaine and morphine) and were randomized to also receive placebo, naltrexone 3 mg, or naltrexone 6 mg. Patients treated with naltrexone experienced shorter duration of pain relief (not statistically significant), however incidence of opioid-induced side effects was reduced. Patients in the naltrexone 6 mg group had lower rates of pruritus, vomiting, and somnolence (all statistically significant) compared to the placebo group.(5) In a double-blind, randomized, placebo-control trial ten recreational opioid users were studied to determine the effects of hydromorphone (4 mg and 16 mg), tramadol (87.5 mg, 175 mg, and 350 mg), and placebo after pretreatment with naltrexone (50 mg) or placebo. Results show that lower doses of hydromorphone and tramadol acted similar to placebo. Hydromorphone 16 mg alone caused euphoria and miosis which were blocked by naltrexone. Tramadol 350 mg produced a lower magnitude of euphoria and miosis compared to hydromorphone. Naltrexone partially diminished the euphoria caused by tramadol, while it enhanced some of the unpleasant monoaminergic effects (flushing, malaise, vomiting).(6) A case report describes a 28 year-old ex-heroin addict who was stable on methadone 100 mg daily and simultaneously stopped using heroin and began drinking alcohol. He was admitted to the hospital for alcohol detoxification and, by mistake, was given naltrexone 100 mg instead of methadone 100 mg. The patient experienced withdrawal symptoms including chills, agitation, muscle and abdominal pain, generalized piloerection, and dilated pupils. Treatment of withdrawal was titrated to treat symptoms and required administration 78 mg of parenteral hydromorphone, after which the patient experienced relief for the following six hours.(8) Intentional administration of an opioid antagonist, naloxone, with opioid analgesics has been performed with close monitoring to lower required opioid dose by inducing withdrawal. Three case reports describe patients who had improved pain relief on significantly reduced doses of opioid analgesics.(8) In a double-blind controlled trial, 267 trauma patients were randomized to receive 0.05 mg/kg intravenous morphine either alone or in combination with 5 mg naltrexone oral suspension. Evaluated endpoints include reduction of pain and incidence of side effects. Results indicate that ultra-low dose naltrexone does not alter opioid requirements for pain control, but does lower incidence of nausea [2 (1.16%) vs 16 (11.6%), p<0.001].(9)

Select Opioids/Sibutramine

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Concurrent administration may result in additive effects on serotonin, resulting in serotonin syndrome.

CLINICAL EFFECTS: Concurrent use of sibutramine and certain opioids may result in serotonin syndrome, a serious and potentially fatal reaction. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(1,3)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Sibutramine has been removed from the market by the European Medicines Agency and by regulatory agencies in a number of countries including Australia, Canada, Hong Kong, India, Thailand, United Kingdom and the United States. The UK manufacturer of sibutramine formerly stated that sibutramine should not be administered with other drugs that raise serotonin levels in the brain, including certain opioids such as dextromethorphan, meperidine, pentazocine, and fentanyl.(2) The US manufacturer of sibutramine stated that in general, sibutramine should not be administered with other serotonergic agents such as dextromethorphan, meperidine, pentazocine, and fentanyl. However, if concurrent administration is clinically indicated, the patient should be appropriately observed.(1) If concurrent therapy is warranted, patients should be monitored for signs and symptoms of serotonin syndrome. Instruct patients to report muscle twitching, tremors, shivering and stiffness, fever, heavy sweating, heart palpitations, restlessness, confusion, agitation, trouble with coordination, or severe diarrhea. Patients in whom serotonin syndrome is suspected should receive immediate medical attention.

DISCUSSION: Sibutramine has been removed from the market by the European Medicines Agency and by regulatory agencies in a number of countries including Australia, Canada, Hong Kong, India, Thailand, United Kingdom and the United States. Because sibutramine inhibits serotonin reuptake and serotonin syndrome has been reported during concomitant use of selective serotonin reuptake inhibitors and certain opioids such as dextromethorphan, meperidine, pentazocine, and fentanyl, the UK manufacturer of sibutramine states that sibutramine should not be administered with these agents.(2)

Selected Opioids/Mifepristone

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Mifepristone is an inhibitor of CYP3A4 and may increase levels and effects of drugs metabolized by this enzyme, including alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, and sufentanil.(1)

CLINICAL EFFECTS: Alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, and sufentanil are particularly susceptible to significant toxicity, including profound sedation, respiratory depression, coma, and/or death.(1,2)

PREDISPOSING FACTORS: Due to the need for continuous therapy and mifepristone's long half-life of 85 hours(1) which leads to accumulation, patients with endogenous Cushing's syndrome may be at an increased risk for toxicity.

PATIENT MANAGEMENT: The US manufacturer of mifepristone for hypercortisolism due to endogenous Cushing's syndrome states use with CYP3A4 substrates with a narrow therapeutic range, including alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, and sufentanil, is contraindicated.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(3) If concomitant use is unavoidable, monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness. Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(4)

DISCUSSION: Administration of mifepristone 1200 mg daily for 10 days followed by a single dose of simvastatin 80 mg led to an increase of simvastatin and simvastatin acid (active metabolite) area-under-curve (AUC) of 10.4-fold and 15.7-fold, respectively.(1) Mifepristone is a time- and concentration-dependent CYP3A4 inhibitor. Single dose mifepristone 200 mg may have a lower risk of inhibiting the metabolism of CYP3A4 substrates, including selected opioids.

Selected Opioids; Dextromethorphan/Selected Maois

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Selected opioids inhibit neural reuptake of serotonin. MAOIs may increase neuronal serotonin concentrations via inhibition of MAO-A.(26)

CLINICAL EFFECTS: The concurrent use of selected opioids with MAOIs has resulted in hypotension, hyperpyrexia, sedation, somnolence, and death. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(26)

PREDISPOSING FACTORS: Higher opioid concentrations as may occur due to inhibition of opioid clearance, patient specific genomic factors (e.g. poor metabolizer status for a P450 enzyme), or high opioid dosage may increase the risk for a severe interaction.

PATIENT MANAGEMENT: Dextromethorphan, diamorphine, meperidine, and tapentadol should not be used in patients taking MAOIs. Use alternative agents for cough or pain. The US manufacturer of Nuedexta(dextromethorphan-quinidine) states Nuedexta is contraindicated within 14 days of MAOI administration.(28) Quinidine increases systemic dextromethorphan concentrations 10 to 20-fold. Other strong CYP2D6 inhibitors such as bupropion, fluoxetine and paroxetine could similarly increase dextromethorphan levels. The US manufacturer of selegiline states that concurrent use with dextromethorphan or meperidine is contraindicated. The US manufacturers of meperidine and tapentadol and the UK manufacturer of diamorphine state that they should not be used concurrently with or within 14 days of taking an MAOI.

DISCUSSION: The interaction between meperidine and MAOIs has been well documented. There are at least two reports of potential interactions between MAOIs and dextromethorphan. Concomitant use of quinidine, a strong CYP2D6 inhibitor, increases systemic dextromethorphan concentrations 10 to 20-fold. Other strong CYP2D6 inhibitors such as bupropion, fluoxetine and paroxetine could similarly increase dextromethorphan levels and risk for serotonin toxicity in patients also receiving MAOIs. Methylene blue, when administered intravenously, has been shown to reach sufficient concentrations to be a potent inhibitor of MAO-A. One or more of the drug pairs linked to this monograph have been included in a list of interactions that should be considered "high-priority" for inclusion and should not be inactivated in EHR systems. This DDI subset was vetted by an expert panel commissioned by the U.S. Office of the National Coordinator (ONC) for Health Information Technology.

Serotonergic Agents/Dapoxetine

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Concurrent administration of dapoxetine with other serotonergic agents may result in additive effects on serotonin, resulting in serotonin syndrome.(1,2)

CLINICAL EFFECTS: Concurrent use of dapoxetine with other serotonergic agents may result in serotonin syndrome, a potentially life-threatening syndrome which may include one or more of the following symptoms: tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(3)

PREDISPOSING FACTORS: Use of multiple drugs which increase serotonin levels is associated with an increased risk for this toxidrome.

PATIENT MANAGEMENT: Dapoxetine should not be administered with other serotonergic agents such as the selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), L-tryptophan, triptans, tramadol, lithium, and/or St. John's Wort.(1,2) Dapoxetine should not be initiated within 14 days of receiving other serotonergic agents. Other serotonergics should not be initiated within 7 days of receiving dapoxetine.(2)

DISCUSSION: This interaction is based on class labeling for these agents. Although there is no clinical documentation for an interaction between dapoxetine and either the elective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), L-tryptophan, triptans, tramadol, lithium, and/or St. John's Wort, caution is still warranted. This syndrome has been reported with the selective serotonin reuptake inhibitors and other serotonergic agents, including sumatriptan and dihydroergotamine.

Slt Serotonergic Opioids (Immediate Release)/Metaxalone

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Concurrent use of serotonergic opioids and metaxalone, a weak monoamine oxidase (MAO) inhibitor, may result in additive CNS depression and additive serotonergic effects.(1,2)

CLINICAL EFFECTS: Concurrent use of opioids and metaxalone may result in profound sedation, respiratory depression, coma, and/or death.(2) The concurrent use of some opioids with serotonergic properties with metaxalone may result in serotonin syndrome. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(2)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects. Treatment with multiple medications which increase serotonin levels or inhibit the metabolism of serotonin are risk factors for serotonin syndrome. Higher opioid concentrations, as may occur due to inhibition of opioid clearance, patient specific genomic factors (e.g. poor metabolizer status for a P450 enzyme), or high opioid dosage may increase the risk for an interaction.

PATIENT MANAGEMENT: Use an alternative analgesic when possible. If concurrent therapy is unavoidable, patients should be monitored for signs and symptoms of serotonin syndrome. Instruct patients to report muscle twitching, tremors, shivering and stiffness, fever, heavy sweating, heart palpitations, restlessness, confusion, agitation, trouble with coordination, or severe diarrhea. If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. If starting a CNS depressant (for an indication other than epilepsy) with an opioid analgesic, prescribe a lower initial dose of the CNS depressant than indicated in the absence of an opioid and titrate based upon clinical response. If an opioid analgesic is indicated in a patient already taking a CNS depressant, prescribe a lower dose of the opioid and titrate based upon clinical response.(2) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(3) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(2) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(4)

DISCUSSION: Between 2002 and 2014, the number of patients receiving an opioid analgesic increased 8%, from 75 million to 81 million patients, and the number of patients receiving a benzodiazepine increased 31%, from 23 million to 30 million patients. During this time, the proportion of patients receiving concurrent therapy increased 31%, from 23 million to 30 million patients.(5) A retrospective cohort study compared the risk of opioid overdose associated with concomitant use of opioids and skeletal muscle relaxants versus opioid use alone. The study examined two types of opioid users (naive opioid use and prevalent opioid use) with and without exposure to skeletal muscle relaxants. The adjusted hazard ratios (HR) were 1.09 and 1.26 in the naive and prevalent opioid user cohorts, respectively, generating a combined estimate of 1.21. The risk increased with treatment duration (less than or equal to 14 days: 0.91; 15-60 days: 1.37; and greater than 60 days: 1.80) and for the use of baclofen and carisoprodol (HR 1.83 and 1.84, respectively). Elevated risk was associated with concomitant users with daily opioid dose greater than 50 mg and benzodiazepine use (HR 1.50 and 1.39, respectively).(6) From 2004 to 2011, the rate of nonmedical use-related emergency room visits involving both opioids and benzodiazepines increased from 11 to 34.2 per 100,000 and drug overdose deaths involving both opioids and benzodiazepines increased from 0.6 to 1.7 per 100,000. The proportion of prescription opioid analgesic deaths which also involved benzodiazepines increased from 18% to 31% during this time.(7) A prospective observational cohort study in North Carolina found that the rates of overdose death among patients co-dispensed opioid analgesics and benzodiazepines were 10 times higher than patients receiving opioid analgesics alone.(8) A case-cohort study of VA data from 2004-2009 found that the risk of death from overdose increased with concomitant opioid analgesics and benzodiazepines. Compared to patients with no history of benzodiazepines, patients with a history of benzodiazepine use (hazard ratio [HR] = 2.33) and patients with a current benzodiazepine prescription (HR=3.86) had an increased risk of fatal overdose.(9) A study found that opioid analgesics contributed to 77% of deaths in which benzodiazepines were determined to be a cause of death and that benzodiazepines contributed to 30% of deaths in which opioid analgesics were determined to be a cause of death. This study also found that other CNS depressants (including barbiturates, antipsychotic and neuroleptic drugs, antiepileptic and antiparkinsonian drugs, anesthetics, autonomic nervous system drugs, and muscle relaxants) were contributory to death in many cases where opioid analgesics were also implicated.(10) A study found that alcohol was involved in 18.5% of opioid analgesic abuse-related ED visits and 22.1 percent of opioid analgesic-related deaths.(11) Although documentation is lacking for some opioids, the FDA recommends health professionals monitor and advise patients to report symptoms of serotonin syndrome in patients receiving analgesic opioids and serotonergic agents.(12) The interaction between meperidine and MAOIs has been well documented. There are two reports of potential interactions between MAOIs and dextromethorphan.(13,14) In another case report, the concurrent use of propoxyphene and phenylzine resulted in sedation and somnolence. The patient had previously taken both agents alone with no adverse effects.(15) Although some studies have shown that morphine does not interact with MAOIs,(16,17) other data indicates that MAOIs markedly potentiate the effect of morphine.(18) Metaxalone is a weak inhibitor of MAO.(1,19)

Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

Agents That May Cause Respiratory Depression/Sodium Oxybate

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Oxybate by itself may be associated with severe somnolence or respiratory depression. Concurrent use with other CNS depressants may further increase the risk for respiratory depression or loss of consciousness.(1-3)

CLINICAL EFFECTS: Concurrent use of sodium oxybate and sedative hypnotics or alcohol may further increase the risk for profound sedation, respiratory depression, coma, and/or death.(1,2) Fatalities have been reported.(3)

PREDISPOSING FACTORS: Based upon FDA evaluation of deaths in patients taking sodium oxybate, risk factors may include: use of multiple drugs which depress the CNS, more rapid than recommended oxybate dose titration, exceeding the maximum recommended oxybate dose, and prescribing for unapproved uses such as fibromyalgia, insomnia or migraine. Note that in oxybate clinical trials for narcolepsy 78% - 85% of patients were also receiving concomitant CNS stimulants.(1-3)

PATIENT MANAGEMENT: Avoid use of concomitant opioids, benzodiazepines, sedating antidepressants, sedating antipsychotics, general anesthetics, or muscle relaxants, particularly when predisposing risk factors are present. If combination use is required, dose reduction or discontinuation of one or more CNS depressants should be considered. If short term use of an opioid or general anesthetic is required, consider interruption of sodium oxybate treatment.(1,2) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(4) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(5)

DISCUSSION: The FDA evaluated sodium oxybate postmarket fatal adverse event reports from the FDA Adverse Event Reporting System(AERS)and from the manufacturer. Although report documentation was not always optimal or complete, useful information was obtained. Factors which may have contributed to fatal outcome: concomitant use of one or more drugs which depress the CNS, more rapid than recommended oxybate dose titration, exceeding the maximum recommended oxybate dose, and prescribing for unapproved uses such as fibromyalgia, insomnia or migraine. Many deaths occurred in patients with serious psychiatric disorders such as depression and substance abuse. Other concomitant diseases may have also contributed to respiratory and CNS depressant effects of oxybate.(3)

Anticholinergics; Opioids/Eluxadoline

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Eluxadoline is a mixed mu-opioid and kappa-opioid agonist and delta-opioid antagonist and may alter or slow down gastrointestinal transit.(1)

CLINICAL EFFECTS: Constipation related adverse events that sometimes required hospitalization have been reported, including the development of intestinal obstruction, intestinal perforation, and fecal impaction.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Avoid use with other drugs that may cause constipation. If concurrent use is necessary, evaluate the patient's bowel function regularly. Monitor for symptoms of constipation and GI hypomotility, including having bowel movements less than three times weekly or less than usual, difficulty having a bowel movement or passing gas, nausea, vomiting, and abdominal pain or distention.(1) Instruct patients to stop eluxadoline and immediately contact their healthcare provider if they experience severe constipation. Loperamide may be used occasionally for acute management of severe diarrhea, but must be discontinued if constipation develops.(1)

DISCUSSION: In phase 3 clinical trials, constipation was the most commonly reported adverse reaction (8%). Approximately 50% of constipation events occurred within the first 2 weeks of treatment while the majority occurred within the first 3 months of therapy. Rates of severe constipation were less than 1% in patients receiving eluxadoline doses of 75 mg and 100 mg.(1)

Meperidine/Clomipramine; Imipramine; Ssris; Snris;

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: The concurrent administration of meperidine with a selective serotonin reuptake inhibitor or a serotonin/norepinephrine reuptake inhibitor (SNRI) may result in additive blockade of serotonin reuptake, resulting in central serotonergic hyperstimulation.(1,2) The combination of meperidine and selective serotonin reuptake inhibitors or SNRIs may also lower the seizure threshold.

CLINICAL EFFECTS: Concurrent administration may result in serotonin syndrome. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(2)

PREDISPOSING FACTORS: Predisposing factors include renal dysfunction and use of multiple agents which increase central serotonin levels. Chronic use of meperidine or high doses of SSRIs or SNRIs would also be expected to increase the risk for serotonin toxicity.

PATIENT MANAGEMENT: Use an alternative analgesic whenever possible, particularly in patients with renal impairment. If concurrent therapy is warranted, patients should be monitored for signs and symptoms of serotonin syndrome, seizure activity. Instruct patients to report muscle twitching, tremors, shivering and stiffness, fever, heavy sweating, heart palpitations, restlessness, confusion, agitation, trouble with coordination, or severe diarrhea.

DISCUSSION: Case reports describe the interaction between meperidine and serotonin-increasing agents.(3-5) Meperidine has long been associated with the risk for serotonin syndrome, particularly when used with monoamine oxidase inhibitors (MAOIs).(6) In addition to SSRIs and SNRIs, clomipramine, a tricyclic antidepressant(TCA) with strong serotonin effects and imipramine, a TCA with more moderate serotonin effects are also included in this monograph.(7)

Meperidine/Selected Cyp3a4 Inhibitors

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: CYP3A4 inhibitors may inhibit the metabolism of meperidine.

CLINICAL EFFECTS: The concurrent administration of a CYP3A4 inhibitor may result in elevated levels of and toxicity from meperidine, including profound sedation, respiratory depression, coma, and/or death.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: If concomitant use is necessary, consider dose reduction of meperidine until stable drug effects are achieved. Monitor patients for respiratory depression and sedation at frequent intervals.(1) If the CYP3A4 inhibitor is discontinued, consider increasing the meperidine dose until stable drug effects are achieved. Monitor for signs of opioid withdrawal.(1) The Australian manufacturer of nirmatrelvir/ritonavir contraindicates co-administration with meperidine.(2) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(3) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(4)

DISCUSSION: Plasma concentrations of the active metabolite normeperidine may be increased by ritonavir (strong CYP3A4 inhibitor).(1) Strong CYP3A4 inhibitors that would be expected to interact with meperidine include: boceprevir, clarithromycin, cobicistat, elvitegravir, idelalisib, indinavir, itraconazole, josamycin, ketoconazole, lonafarnib, lopinavir, mibefradil, nelfinavir, nirmatrelvir, paritaprevir, posaconazole, relacorilant, ribociclib, saquinavir, telaprevir, telithromycin, tipranavir, troleandomycin, tucatinib, voriconazole.(5) Moderate CYP3A4 inhibitors include: erythromycin and fluconazole.(5)

Meperidine/Serotonergic Cyp3a4 Inhibitors

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: CYP3A4 inhibitors such as fluvoxamine and nefazodone may inhibit the metabolism of meperidine.(1-3) Meperidine inhibits the reuptake of serotonin.(1) Fluvoxamine and nefazodone also inhibit the reuptake of serotonin.(2,3)

CLINICAL EFFECTS: Concurrent administration may result in elevated levels of and toxicity from meperidine.(1) Concurrent administration could also increase the risk for serotonin syndrome. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(4)

PREDISPOSING FACTORS: Serotonin syndrome risk is dose-related. Higher systemic concentrations of meperidine would be predicted to increase risk for serotonin toxicity. Concomitant therapy with other agents which increase brain serotonin concentrations may also increase risk.(1-4) Renal dysfunction and chronic use of meperidine would be expected to increase the risk for serotonin toxicity due to meperidine.(1)

PATIENT MANAGEMENT: If concomitant use is necessary, consider dose reduction of meperidine until stable drug effects are achieved. Monitor patients for respiratory depression and sedation at frequent intervals.(1) If the CYP3A4 inhibitor is discontinued, consider increasing the meperidine dose until stable drug effects are achieved. Monitor for signs of opioid withdrawal.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(5) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(6) Assess patient for predisposing risk factors of serotonin syndrome and monitor accordingly. The manufacturer of meperidine recommends careful monitoring for signs and symptoms of serotonin syndrome when a metabolic inhibitor or another serotoninergic agent is started, or when the dose of either agent is increased.(1-4)

DISCUSSION: Plasma concentrations of the active metabolite normeperidine may be increased by ritonavir (strong CYP3A4 inhibitor).(1)

Meperidine/Tramadol

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: The concurrent administration of tramadol(1) with meperidine(2) may result in additive blockade of serotonin reuptake, leading to central serotonergic hyperstimulation, as well as additive sedation, respiratory depression, coma, and/or death.

CLINICAL EFFECTS: Concurrent administration may increase the risk for adverse events, including serotonin syndrome, sedation, and respiratory depression. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(3)

PREDISPOSING FACTORS: Patients who are CYP2D6 ultrarapid metabolizers have accelerated conversion of tramadol to its active metabolite, M1, and may be at higher risk of sedation and respiratory depression.(1) Treatment with multiple medications which increase serotonin levels or with medications which inhibit the metabolism of serotonin increasing drugs are risk factors for serotonin syndrome.(3) A genetic defect in CYP2D6 leading to the slow metabolizer phenotype may increase the risk for serotonin syndrome due to tramadol. Renal dysfunction and chronic use of meperidine would be expected to increase the risk for serotonin toxicity due to meperidine.

PATIENT MANAGEMENT: Use an alternative to meperidine whenever possible, particularly in patients with renal impairment. If concurrent therapy of tramadol with meperidine is warranted, patients should be closely monitored for signs and symptoms of sedation, respiratory depression and serotonin syndrome. One or both agents may need to be discontinued. Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression. Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(2)

DISCUSSION: There are a number of serotonin syndrome case reports following the addition of tramadol to a stable selective serotonin reuptake inhibitor regimen. The syndrome developed between 12 hours to 3 weeks after the initiation of tramadol therapy. Patients recovered after tramadol and/or the SSRI/SNRI was discontinued.(4-16) One patient also developed mania.(4) Another patient developed nightmares and hallucinations after taking concurrent tramadol and paroxetine for 56 days.(5) One author suggests that although the combination of tramadol and SSRIs or SNRIs is associated with a risk for serotonin syndrome, given the high rate of co-prescribing for the combination it is an uncommon outcome.(17) Case reports describe the interaction between meperidine and serotonin-increasing agents.(18-20) Although there are no reports of serotonin syndrome specifically with the combination of tramadol and meperidine, both drugs inhibit serotonin reuptake and caution is still warranted.

Selected Opioids/Ceritinib; Crizotinib

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Ceritinib(1) and crizotinib(2) inhibit CYP3A4, and thus may inhibit the metabolism of agents processed by this isoenzyme, including alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, and sufentanil.

CLINICAL EFFECTS: Concurrent use of ceritinib(1) or crizotinib(2) with alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, or sufentanil may lead to elevated drug levels and increased side effects of the opioid, including profound sedation, respiratory depression, coma, and/or death.(1-3)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Avoid coadministration of sensitive or narrow therapeutic window CYP3A4 substrates such as alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, or sufentanil with ceritinib and crizotinib. If concomitant use is unavoidable, dosage adjustments of the opioid should be considered when initiating or discontinuing ceritinib(1) or crizotinib.(2) Patients maintained on ceritinib or crizotinib may need lower initial doses of opioid medications. Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(5) Monitor patients receiving concurrent therapy for adverse affects, including unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness. Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(6)

DISCUSSION: In a study, ceritinib (750 mg daily for 3 weeks) increased the area-under-curve (AUC) and maximum concentration (Cmax) of midazolam (a CYP3A4 substrate) by 5.4-fold and 1.8-fold, respectively, compared to midazolam alone.(1) Crizotinib (250 mg twice daily for 28 days) increased the AUC of oral midazolam by 3.7-fold.(2) Thus, ceritinib(1) and crizotinib(2) are expected to increase levels of opioids metabolized by CYP3A4.

Selected Opioids; Dextromethorphan-Quinidine/Linezolid

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Selected opioids inhibit neural reuptake of serotonin. Linezolid may increase neuronal serotonin concentrations via inhibition of MAO-A.(23)

CLINICAL EFFECTS: The concurrent use of some opioids with MAOIs has resulted in serotonin syndrome. Severe cases of serotonin syndrome may be fatal. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(23)

PREDISPOSING FACTORS: Higher opioid concentrations (e.g., due to inhibition of opioid clearance, patient specific genomic factors such as poor metabolizer status for a cytochrome P450 enzyme, or high opioid dosage) may increase the risk for a severe interaction.

PATIENT MANAGEMENT: The manufacturer of linezolid states that linezolid should not be used in patients taking serotonergic agents unless clinically appropriate and patients are closely monitored for signs and symptoms of serotonin syndrome.(18) The US manufacturer of Nuedexta (dextromethorphan-quinidine) states Nuedexta is contraindicated within 14 days of MAOI administration.(19) Diamorphine, meperidine, and tapentadol should not be used in patients taking MAOIs, but if concomitant use of serotonergic drugs like linezolid is warranted, frequently evaluate the patient, particularly during treatment initiation and dose adjustment.(20-21) Use alternative agents for cough or pain.

DISCUSSION: The interaction between meperidine and MAOIs has been well documented. There is one case report of serotonin syndrome with concurrent meperidine and linezolid. Many authors state that linezolid is a weak MAOI and rarely causes serotonin toxicity. Cases of serotonin toxicity were rapidly reversible with discontinuation of the offending agent(s) and supportive care. Some authors suggest that use of serotonergic medications should not preclude the use of linezolid but that the clinical situation should be assessed. If concurrent use or use of linezolid without a washout is warranted, the patient should be closely monitored.(22-27)

Moderate Interaction: Assess the risk to the patient and take action as needed.

Agents With Hyponatremia Risk/Desmopressin

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Carbamazepine, chlorpromazine, lamotrigine, NSAIDs, opioids, SSRIs, thiazide diuretics, and/or tricyclic antidepressants increase the risk of hyponatremia.(1-3)

CLINICAL EFFECTS: Concurrent use may increase the risk of hyponatremia with desmopressin.(1-3)

PREDISPOSING FACTORS: Predisposing factors for hyponatremia include: polydipsia, renal impairment (eGFR < 50 ml/min/1.73m2), illnesses that can cause fluid/electrolyte imbalances, age >=65, medications that cause water retention and/or increase the risk of hyponatremia (glucocorticoids, loop diuretics).

PATIENT MANAGEMENT: The concurrent use of agents with a risk of hyponatremia with desmopressin may increase the risk of hyponatremia. If concurrent use is deemed medically necessary, make sure serum sodium levels are normal before beginning therapy and consider using the desmopressin nasal 0.83 mcg dose. Consider measuring serum sodium levels more frequently than the recommended intervals of: within 7 days of concurrent therapy initiation, one month after concurrent therapy initiation and periodically during treatment. Counsel patients to report symptoms of hyponatremia, which may include: headache, nausea/vomiting, feeling restless, fatigue, drowsiness, dizziness, muscle cramps, changes in mental state (confusion, decreased awareness/alertness), seizures, coma, and trouble breathing. Counsel patients to limit the amount of fluids they drink in the evening and night-time and to stop taking desmopressin if they develop a stomach/intestinal virus with nausea/vomiting or any nose problems (blockage, stuffy/runny nose, drainage).(1)

DISCUSSION: In clinical trials of desmopressin for the treatment of nocturia, 4 of 5 patients who developed severe hyponatremia (serum sodium <= 125 mmol/L) were taking systemic or inhaled glucocorticoids. Three of these patients were also taking NSAIDs and one was receiving a thiazide diuretic.(2) Drugs associated with hyponatremia may increase the risk, including loop diuretics, carbamazepine, chlorpromazine, glucocorticoids, lamotrigine, NSAIDs, opioids, SSRIs, thiazide diuretics, and/or tricyclic antidepressants.(1,3-4)

Meperidine (Immediate Release)/Chlorpromazine; Promethazine

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Concurrent use of opioids such as meperidine and antipsychotics such as chlorpromazine or phenothiazine derivatives such as promethazine may result in additive CNS depression.(1)

CLINICAL EFFECTS: Concurrent use of opioids such as meperidine and antipsychotics such as chlorpromazine or phenothiazine derivatives such as promethazine may result in profound sedation, respiratory depression, coma, and/or death.(1)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects.

PATIENT MANAGEMENT: Limit prescribing opioid analgesics such as meperidine with CNS depressants such as chlorpromazine or promethazine to patients for whom alternatives are ineffective, not tolerated, or would be otherwise inadequate to provide sufficient management of pain.(1) If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. If starting a CNS depressant with an opioid analgesic, prescribe a lower initial dose of the CNS depressant than indicated in the absence of an opioid and titrate based upon clinical response. If an opioid analgesic is indicated in a patient already taking a CNS depressant, prescribe a lower dose of the opioid and titrate based upon clinical response.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(2) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(3)

DISCUSSION: A nested case-control study looked at the relationship between antipsychotic use and risk of acute respiratory failure. Current use of antipsychotics was associated with a 2.33-fold increase in risk of respiratory failure compared to no use of antipsychotics. The risk was also significantly increased in patients with recent use of antipsychotics (within the past 15-30 days, OR = 1.79) and recent past use (within 31-90 days OR = 1.41). The risk increased with higher doses and longer duration of use.(4) Between 2002 and 2014, the number of patients receiving an opioid analgesic increased 8%, from 75 million to 81 million patients, and the number of patients receiving a benzodiazepine increased 31%, from 23 million to 30 million patients. During this time, the proportion of patients receiving concurrent therapy increased 31%, from 23 million to 30 million patients.(5) From 2004 to 2011, the rate of nonmedical use-related emergency room visits involving both opioids and benzodiazepines increased from 11 to 34.2 per 100,000 and drug overdose deaths involving both opioids and benzodiazepines increased from 0.6 to 1.7 per 100,000. The proportion of prescription opioid analgesic deaths which also involved benzodiazepines increased from 18% to 31% during this time.(6) A prospective observational cohort study in North Carolina found that the rates of overdose death among patients co-dispensed opioid analgesics and benzodiazepines were 10 times higher than patients receiving opioid analgesics alone.(7) A case-cohort study of VA data from 2004-2009 found that the risk of death from overdose increased with concomitant opioid analgesics and benzodiazepines. Compared to patients with no history of benzodiazepines, patients with a history of benzodiazepine use (hazard ratio [HR] = 2.33) and patients with a current benzodiazepine prescription (HR=3.86) had an increased risk of fatal overdose.(8) A study found that opioid analgesics contributed to 77% of deaths in which benzodiazepines were determined to be a cause of death and that benzodiazepines contributed to 30% of deaths in which opioid analgesics were determined to be a cause of death. This study also found that other CNS depressants (including barbiturates, antipsychotic and neuroleptic drugs, antiepileptic and antiparkinsonian drugs, anesthetics, autonomic nervous system drugs, and muscle relaxants) were contributory to death in many cases where opioid analgesics were also implicated.(9) A study found that alcohol was involved in 18.5% of opioid analgesic abuse-related ED visits and 22.1 percent of opioid analgesic-related deaths.(10)

Meperidine (Ir)/Selected Antipsychotics; Phenothiazines

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Concurrent use of opioids such as meperidine and antipsychotics, including phenothiazine derivatives, may result in additive CNS depression.(1)

CLINICAL EFFECTS: Concurrent use of opioids such as meperidine and other CNS depressants, such as antipsychotics, including phenothiazine derivatives, may result in profound sedation, respiratory depression, coma, and/or death.(1)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects.

PATIENT MANAGEMENT: Limit prescribing opioid analgesics such as meperidine with CNS depressants such as antipsychotics, including phenothiazine derivatives, to patients for whom alternatives are ineffective, not tolerated, or would be otherwise inadequate to provide sufficient management of pain.(1) If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. If starting a CNS depressant (for an indication other than epilepsy) with an opioid analgesic, prescribe a lower initial dose of the CNS depressant than indicated in the absence of an opioid and titrate based upon clinical response. If an opioid analgesic is indicated in a patient already taking a CNS depressant, prescribe a lower dose of the opioid and titrate based upon clinical response.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(2) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(3)

DISCUSSION: A nested case-control study looked at the relationship between antipsychotic use and risk of acute respiratory failure. Current use of antipsychotics was associated with a 2.33-fold increase in risk of respiratory failure compared to no use of antipsychotics. The risk was also significantly increased in patients with recent use of antipsychotics (within the past 15-30 days, OR = 1.79) and recent past use (within 31-90 days OR = 1.41). The risk increased with higher doses and longer duration of use.(4) Between 2002 and 2014, the number of patients receiving an opioid analgesic increased 8%, from 75 million to 81 million patients, and the number of patients receiving a benzodiazepine increased 31%, from 23 million to 30 million patients. During this time, the proportion of patients receiving concurrent therapy increased 31%, from 23 million to 30 million patients.(5) From 2004 to 2011, the rate of nonmedical use-related emergency room visits involving both opioids and benzodiazepines increased from 11 to 34.2 per 100,000 and drug overdose deaths involving both opioids and benzodiazepines increased from 0.6 to 1.7 per 100,000. The proportion of prescription opioid analgesic deaths which also involved benzodiazepines increased from 18% to 31% during this time.(6) A prospective observational cohort study in North Carolina found that the rates of overdose death among patients co-dispensed opioid analgesics and benzodiazepines were 10 times higher than patients receiving opioid analgesics alone.(7) A case-cohort study of VA data from 2004-2009 found that the risk of death from overdose increased with concomitant opioid analgesics and benzodiazepines. Compared to patients with no history of benzodiazepines, patients with a history of benzodiazepine use (hazard ratio [HR] = 2.33) and patients with a current benzodiazepine prescription (HR=3.86) had an increased risk of fatal overdose.(8) A study found that opioid analgesics contributed to 77% of deaths in which benzodiazepines were determined to be a cause of death and that benzodiazepines contributed to 30% of deaths in which opioid analgesics were determined to be a cause of death. This study also found that other CNS depressants (including barbiturates, antipsychotic and neuroleptic drugs, antiepileptic and antiparkinsonian drugs, anesthetics, autonomic nervous system drugs, and muscle relaxants) were contributory to death in many cases where opioid analgesics were also implicated.(9) A study found that alcohol was involved in 18.5% of opioid analgesic abuse-related ED visits and 22.1 percent of opioid analgesic-related deaths.(10)

Meperidine Injection/Doxepin (> 25 Mg)

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: The concurrent administration of meperidine with other serotonergic agents may result in additive serotonin effects, resulting in central serotonergic hyperstimulation.(1) Meperidine, its nor-meperidine metabolite, and antidepressants may also lower the seizure threshold.

CLINICAL EFFECTS: Concurrent administration of meperidine and higher dose doxepin may result in serotonin syndrome or seizures. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(1)

PREDISPOSING FACTORS: Renal dysfunction may increase seizure risk due to elevated nor-meperidine (toxic metabolite) concentrations.(2,3) Use of multiple serotonergic agents increases the risk for serotonin toxicity.(1)

PATIENT MANAGEMENT: Meperidine injection patients with renal impairment who also receive concomitant therapy with higher dose doxepin should be monitored for signs and symptoms of serotonin syndrome or seizure activity. Meperidine may need to be discontinued. If concurrent therapy is warranted, patients should be monitored for signs and symptoms of serotonin syndrome. Instruct patients to report muscle twitching, tremors, shivering and stiffness, fever, heavy sweating, heart palpitations, restlessness, confusion, agitation, trouble with coordination, or severe diarrhea.

DISCUSSION: Although this interaction is theoretically possible, no case reports describing this interaction have been found.

Meperidine/Amphetamines

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Opioids and stimulants exhibit opposing effects on the CNS.(1) Amphetamines may affect serotonin release and/or reuptake, depending on their molecular structure. Ring substitution tends to increase amphetamine-induced release of endogenous serotonin. However, the effect on serotonin release may also be dose related and is more likely if the amphetamine is taken in doses greater than those approved and generally employed in treating attention-deficit-hyperactivity-disorder, or if abused, especially over long periods of time.(1) Meperidine blocks serotonin reuptake. Concurrent administration of amphetamines with meperidine may produce additive effects on serotonin, resulting in serotonin syndrome.(2,3)

CLINICAL EFFECTS: Opposing CNS effects of opioids and stimulants may compromise the effectiveness of both agents and mask opioid overdose symptoms such as drowsiness and inability to focus. Concurrent use of amphetamines with meperidine may increase the risk of serotonin syndrome, a potentially life-threatening syndrome which may include one or more of the following symptoms: tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(4)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects. High doses or long-term abuse of amphetamines may increase the risk of this interaction. Renal dysfunction and chronic use of meperidine would also be expected to increase the risk for serotonin toxicity. Use of multiple drugs which increase serotonin levels is associated with an increased risk for this toxidrome.

PATIENT MANAGEMENT: Limit prescribing meperidine with CNS stimulants such as amphetamines to patients for whom alternatives are ineffective, not tolerated, or would be otherwise inadequate to provide sufficient management of pain.(1) Concurrent use of amphetamines with meperidine should be approached with appropriate monitoring, especially during therapy initiation and dose increase. Instruct patients receiving concurrent therapy to report any signs or symptoms of serotonin syndrome immediately. Consider initiating amphetamines or meperidine at lower doses and monitor for signs and symptoms of serotonin syndrome. Discontinue one or both medications if symptoms occur. Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with stimulants. Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Discuss opioid reversal agents (e.g., naloxone, nalmefene) to patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing opioid reversal agents (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(1) Monitor patients receiving concurrent therapy for signs of substance abuse.

DISCUSSION: A total of 70,237 persons died from drug overdoses in the United States in 2017; approximately two thirds of these deaths involved an opioid.(2). The CDC analyzed 2016-2017 changes in age-adjusted death rates involving cocaine and psychostimulants by demographic characteristics, urbanization levels, U.S. Census region, 34 states, and the District of Columbia (DC). The CDC also examined trends in age-adjusted cocaine-involved and psychostimulant-involved death rates from 2003 to 2017 overall, as well as with and without co-involvement of opioids. Among all 2017 drug overdose deaths, 13,942 (19.8%) involved cocaine, and 10,333 (14.7%) involved psychostimulants. Death rates increased from 2016 to 2017 for both drug categories across demographic characteristics, urbanization levels, Census regions, and states. In 2017, opioids were involved in 72.7% and 50.4% of cocaine-involved and psychostimulant-involved overdoses, respectively, and the data suggest that increases in cocaine-involved overdose deaths from 2012 to 2017 were driven primarily by synthetic opioids.(7) There was opioid co-involvement in 72.7 percent of cocaine and 50.4 percent of stimulant-involved overdose deaths. This was largely driven by synthetic opioids such as fentanyl. However, stimulant-involved overdose without opioid co-involvement is also increasing.(6)

Meperidine/Cyclobenzaprine

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Cyclobenzaprine and meperidine may have additive effects on serotonin levels.(1,2)

CLINICAL EFFECTS: Concurrent administration of cyclobenzaprine with meperidine may result in serotonin syndrome. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.

PREDISPOSING FACTORS: Predisposing factors include elderly, renal or hepatic dysfunction, and use of multiple agents which increase central serotonin levels. Chronic use of cyclobenzaprine or meperidine would also be expected to increase the risk for serotonin toxicity.(1,2)

PATIENT MANAGEMENT: The US manufacturer of cyclobenzaprine recommends limiting use to short term duration, no more than two to three weeks. The US manufacturer of meperidine states that it should not be used for treatment of chronic pain. Use alternative therapy whenever possible, particularly in patients with renal or hepatic impairment.(1,2) If concurrent therapy is warranted, patients should be monitored for signs and symptoms of serotonin syndrome, and seizure activity. Instruct patients to report muscle twitching, tremors, shivering and stiffness, fever, heavy sweating, heart palpitations, restlessness, confusion, agitation, trouble with coordination, or severe diarrhea.

DISCUSSION: Case reports documenting serotonin syndrome with cyclobenzaprine and other serotonergic agents are described. The risk of serotonin syndrome with cyclobenzaprine may occur based on serotonin activity of both agents.(3,4) A case report of a 70 year old female on phenelzine (non-selective MAOI) 15 mg four times daily for several years developed serotonin syndrome after the third dose of cyclobenzaprine 10 mg three times daily. After discontinuation of both cyclobenzaprine and phenelzine, symptoms resolved within three days. Within the following month, the patient was restarted on phenelzine without any further sequelae.(5) A case report of a 53 year old male on duloxetine (SNRI) 60 mg daily developed symptoms of serotonin syndrome shortly after initiation of cyclobenzaprine 10 mg three times daily. Both cyclobenzaprine and duloxetine were stopped and cyproheptadine was given with resolution of symptoms.(5) A case report of a 27 year old female on escitalopram (SSRI) 10 mg daily presented with serotonin syndrome after an overdose of 5-6 cyclobenzaprine 10 mg tablets. The patient was treated with symptomatic care and cyproheptadine with resolution of symptoms on day two and discharged with instructions to discontinue cyclobenzaprine use.(6) Case reports describe the interaction between meperidine and serotonin-increasing agents.(7-9) Although there are no reports of serotonin syndrome specifically with the combination of cyclobenzaprine and meperidine, both drugs inhibit serotonin reuptake and caution is still warranted.

Meperidine/Lithium

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: The combination of lithium with meperidine may have additive effects on serotonin levels.(1,2)

CLINICAL EFFECTS: Some patients may develop an increase in serotonergic activity in the CNS, which could result in serotonin syndrome. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(3)

PREDISPOSING FACTORS: Renal dysfunction and chronic use of meperidine would be expected to increase the risk for serotonin toxicity. The use of multiple drugs that increase serotonin levels is associated with an increased risk for this toxidrome.

PATIENT MANAGEMENT: Patients receiving concurrent therapy should be observed for signs of serotonergic side effects. When clinically appropriate, consider monitoring serum concentrations for toxicity. Counsel patients to report new or worsening muscle twitching, tremors, shivering or stiffness, fever, heavy sweating, heart palpitations, restlessness, confusion, agitation, decreased coordination, or severe diarrhea. Discontinue one or both medications if symptoms occur. Although toxicity has been reported, based upon cases and interaction studies the likelihood of a drug-drug interaction appears to be uncommon, perhaps rare.(4)

DISCUSSION: Serotonin syndrome has been reported from the combination of lithium with serotonergic drugs, including SSRIs, SNRIs, and tramadol. Although there are no reports of serotonin syndrome specifically with the combination of lithium and meperidine, a pharmacological basis for an interaction exists, and caution is still warranted. While toxicity has been reported, based upon cases and interaction studies the likelihood of a drug-drug interaction appears to be uncommon, perhaps rare.(4) Some of the reported cases may represent drug-disease interactions (e.g. mania with lithium and antidepressant).

Meperidine/Methylphenidate

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Opioids and methylphenidate exhibit opposing effects on the CNS.(1)

CLINICAL EFFECTS: Opposing CNS effects of opioids and stimulants may compromise the effectiveness of both agents and mask opioid overdose symptoms such as drowsiness and inability to focus.

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects.

PATIENT MANAGEMENT: Limit prescribing meperidine with CNS stimulants such as methylphenidate to patients for whom alternatives are ineffective, not tolerated, or would be otherwise inadequate to provide sufficient management of pain. If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(1) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness. Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program). Monitor patients receiving concurrent therapy for signs of substance abuse.

DISCUSSION: A total of 70,237 persons died from drug overdoses in the United States in 2017; approximately two thirds of these deaths involved an opioid.(2). The CDC analyzed 2016-2017 changes in age-adjusted death rates involving cocaine and psychostimulants by demographic characteristics, urbanization levels, U.S. Census region, 34 states, and the District of Columbia (DC). The CDC also examined trends in age-adjusted cocaine-involved and psychostimulant-involved death rates from 2003 to 2017 overall, as well as with and without co-involvement of opioids. Among all 2017 drug overdose deaths, 13,942 (19.8%) involved cocaine, and 10,333 (14.7%) involved psychostimulants. Death rates increased from 2016 to 2017 for both drug categories across demographic characteristics, urbanization levels, Census regions, and states. In 2017, opioids were involved in 72.7% and 50.4% of cocaine-involved and psychostimulant-involved overdoses, respectively, and the data suggest that increases in cocaine-involved overdose deaths from 2012 to 2017 were driven primarily by synthetic opioids.(3) There was opioid co-involvement in 72.7 percent of cocaine and 50.4 percent of stimulant-involved overdose deaths. This was largely driven by synthetic opioids such as fentanyl. However, stimulant-involved overdose without opioid co-involvement is also increasing.(2)

Meperidine; Tramadol/Trazodone (<= 50 Mg)

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Meperidine and tramadol inhibit the reuptake of serotonin.(1,2) Metabolism of trazodone leads to formation of the active metabolite, m-chlorophenylpiperazine (mCPP) which is an agonist at a variety of serotonin receptors.(3,4) Both tramadol and mCPP are metabolized by CYP2D6.(2,4-6)

CLINICAL EFFECTS: Concurrent administration could increase the risk for serotonin syndrome. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(7)

PREDISPOSING FACTORS: Serotonin syndrome risk is dose-related. Higher systemic concentrations of meperidine, tramadol or mCPP would be predicted to increase risk for serotonin toxicity. Concomitant therapy with other agents which increase brain serotonin concentrations may also increase risk.(1-3,7) Renal dysfunction and chronic use of meperidine would be expected to increase the risk for serotonin toxicity due to meperidine. Concomitant treatment with inhibitors of CYP2D6 (e.g. bupropion, cinacalcet, duloxetine, fluoxetine, paroxetine, quinidine, or systemic terbinafine) may also increase mCPP and tramadol concentrations, increasing risk for serotonin toxicity. Patients who are poor metabolizers at CYP2D6 would be expected to have higher tramadol and mCPP concentrations compared with extensive metabolizers.(2,3)

PATIENT MANAGEMENT: Assess patient for predisposing risk factors and monitor accordingly. Manufacturers of meperidine, tramadol and trazodone recommend careful monitoring for signs and symptoms of serotonin syndrome when a metabolic inhibitor or another serotoninergic agent is started, or when the dose of either agent is increased.(1-3)

DISCUSSION: Meperidine, tramadol and trazodone have each been associated with serotonin syndrome when given concurrently with one or more serotoninergic agents.(1-3) MCPP has been associated with serotonin syndrome when used as a probe of central serotonin function in human investigational studies.(8) CYP3A4 converts trazodone to mCPP which is then converted to an inactive metabolite via CYP2D6.(3,4)

Meperidine; Tramadol/Trazodone (> 50 Mg)

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Tramadol inhibits the reuptake of serotonin.(1,2) Metabolism of trazodone leads to formation of a common active metabolite, m-chlorophenylpiperazine (mCPP) which is an agonist at a variety of serotonin receptors.(3-5) Both tramadol and mCPP are metabolized by CYP2D6.(1,3-5)

CLINICAL EFFECTS: Concurrent administration could increase the risk for serotonin syndrome. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(6)

PREDISPOSING FACTORS: Serotonin syndrome risk is dose-related. Higher systemic concentrations of meperidine, tramadol or mCPP would be predicted to increase risk for serotonin toxicity. Concomitant therapy with other agents which increase brain serotonin concentrations may also increase risk.(1-3,6) Renal dysfunction and chronic use of meperidine would be expected to increase the risk for serotonin toxicity due to meperidine. Concomitant treatment with inhibitors of CYP2D6 (e.g. bupropion, cinacalcet, duloxetine, fluoxetine, paroxetine, quinidine, or systemic terbinafine) may also increase mCPP and tramadol concentrations, increasing risk for serotonin toxicity. Patients who are poor metabolizers at CYP2D6 would be expected to have higher tramadol and mCPP concentrations compared with extensive metabolizers.(1,3)

PATIENT MANAGEMENT: Assess patient for predisposing risk factors and monitor accordingly. Manufacturers of meperidine, tramadol and trazodone recommend careful monitoring for signs and symptoms of serotonin syndrome when a metabolic inhibitor or another serotoninergic agent is started, or when the dose of either agent is increased.(1-3)

DISCUSSION: Meperidine, tramadol, and trazodone have each been associated with serotonin syndrome when given concurrently with one or more serotoninergic agents.(1-3) MCPP has been associated with serotonin syndrome when used as a probe of central serotonin function in human investigational studies.(7) CYP3A4 converts trazodone to mCPP which is then converted to an inactive metabolite via CYP2D6.(3-4)

Opioids (Immediate Release)/Benzodiazepines

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Concurrent use of opioids and benzodiazepines may result in additive CNS depression.(1)

CLINICAL EFFECTS: Concurrent use of opioids and other CNS depressants, such as benzodiazepines, may result in profound sedation, respiratory depression, coma, and/or death.(1)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects.

PATIENT MANAGEMENT: Limit prescribing opioid analgesics with CNS depressants such as benzodiazepines to patients for whom alternatives are ineffective, not tolerated, or would be otherwise inadequate to provide sufficient management of pain.(1) If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. If starting a CNS depressant (for an indication other than epilepsy) with an opioid analgesic, prescribe a lower initial dose of the CNS depressant than indicated in the absence of an opioid and titrate based upon clinical response. If an opioid analgesic is indicated in a patient already taking a CNS depressant, prescribe a lower dose of the opioid and titrate based upon clinical response.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(2) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(3)

DISCUSSION: Between 2002 and 2014, the number of patients receiving an opioid analgesic increased 8%, from 75 million to 81 million patients, and the number of patients receiving a benzodiazepine increased 31%, from 23 million to 30 million patients. During this time, the proportion of patients receiving concurrent therapy increased 31%, from 23 million to 30 million patients.(4) From 2004 to 2011, the rate of nonmedical use-related emergency room visits involving both opioids and benzodiazepines increased from 11 to 34.2 per 100,000 and drug overdose deaths involving both opioids and benzodiazepines increased from 0.6 to 1.7 per 100,000. The proportion of prescription opioid analgesic deaths which also involved benzodiazepines increased from 18% to 31% during this time.(5) A prospective observational cohort study in North Carolina found that the rates of overdose death among patients co-dispensed opioid analgesics and benzodiazepines were 10 times higher than patients receiving opioid analgesics alone.(6) A case-cohort study of VA data from 2004-2009 found that the risk of death from overdose increased with concomitant opioid analgesics and benzodiazepines. Compared to patients with no history of benzodiazepines, patients with a history of benzodiazepine use (hazard ratio [HR] = 2.33) and patients with a current benzodiazepine prescription (HR=3.86) had an increased risk of fatal overdose.(7) A study found that opioid analgesics contributed to 77% of deaths in which benzodiazepines were determined to be a cause of death and that benzodiazepines contributed to 30% of deaths in which opioid analgesics were determined to be a cause of death. This study also found that other CNS depressants (including barbiturates, antipsychotic and neuroleptic drugs, antiepileptic and antiparkinsonian drugs, anesthetics, autonomic nervous system drugs, and muscle relaxants) were contributory to death in many cases where opioid analgesics were also implicated.(8) A study found that alcohol was involved in 18.5% of opioid analgesic abuse-related ED visits and 22.1 percent of opioid analgesic-related deaths.(9) A study of 315,428 privately insured patients who filled at least one prescription for an opioid from 2001 to 2013 were enrolled in a retrospective study. Concurrent use of a benzodiazepine was recorded as having at least one day of overlap in a given calendar year. Baseline characteristics among opioid users with concurrent use of a benzodiazepine were older (44.5 v. 42.4, p<0.001), less likely to be men (35% v. 43%, p<0.001), and had a higher prevalence rate of every comorbidity examined (p<0.001). The proportion of opioid users with concurrent benzodiazepine use nearly doubled from 9% in 2001 to 17% in 2013. The primary outcome was an emergency room visit or inpatient admission for opioid overdose within a calendar year. Among all opioid users, the annual adjusted incidence for the primary outcome was 1.16% without concurrent benzodiazepine use compared to 2.42% with concurrent benzodiazepine use (OR 2.14; 95% CI 2.05-2.24; p<0.001). Intermittent opioid users (1.45% v. 1.02%; OR 1.42; 95% CI 1.33-1.51; p<0.001) and chronic opioid users (5.36% v. 3.13%; OR 1.81; 95% CI 1.67-1.96; p<0.001) also experienced a higher adjusted incidence of the primary outcome with concurrent benzodiazepine use compared to without concurrent benzodiazepine use, respectively.(10) In a nested case-control study of adults with a new opioid dispensing between 2010-2018, patients with concurrent use of an opioid with a benzodiazepine were significantly more likely to have opioid-related overdose compared to patients receiving opioids, benzodiazepines, or neither (OR 9.28; 95% CI 7.87, 10.93). Longer concurrent use of 1-7, 8-30, and 31-90 days was associated with 4.6, 12.1, and 26.7-fold higher likelihood of opioid-related overdose (p<0.01). Patients with overlapping prescriptions during previous 0-30, 31-60, and 61-90 days were 13.2, 6.0, and 3.2-times more likely to experience an overdose (p<0.01).(11)

Opioids (Immediate Release)/Muscle Relaxants

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Concurrent use of opioids and muscle relaxants may result in additive CNS depression.(1)

CLINICAL EFFECTS: Concurrent use of opioids and other CNS depressants, such as muscle relaxants, may result in profound sedation, respiratory depression, coma, and/or death.(1)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects.

PATIENT MANAGEMENT: Limit prescribing opioid analgesics with CNS depressants such as muscle relaxants to patients for whom alternatives are ineffective, not tolerated, or would be otherwise inadequate to provide sufficient management of pain.(1) If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. If starting a CNS depressant (for an indication other than epilepsy) with an opioid analgesic, prescribe a lower initial dose of the CNS depressant than indicated in the absence of an opioid and titrate based upon clinical response. If an opioid analgesic is indicated in a patient already taking a CNS depressant, prescribe a lower dose of the opioid and titrate based upon clinical response.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(2) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(3)

DISCUSSION: Between 2002 and 2014, the number of patients receiving an opioid analgesic increased 8%, from 75 million to 81 million patients, and the number of patients receiving a benzodiazepine increased 31%, from 23 million to 30 million patients. During this time, the proportion of patients receiving concurrent therapy increased 31%, from 23 million to 30 million patients.(4) A retrospective cohort study compared the risk of opioid overdose associated with concomitant use of opioids and skeletal muscle relaxants versus opioid use alone. The study examined two types of opioid users (naive opioid use and prevalent opioid use) with and without exposure to skeletal muscle relaxants. The adjusted hazard ratios (HR) were 1.09 and 1.26 in the naive and prevalent opioid user cohorts, respectively, generating a combined estimate of 1.21. The risk increased with treatment duration (less than or equal to 14 days: 0.91; 15-60 days: 1.37; and greater than 60 days: 1.80) and for the use of baclofen and carisoprodol (HR 1.83 and 1.84, respectively). Elevated risk was associated with concomitant users with daily opioid dose greater than 50 mg and benzodiazepine use (HR 1.50 and 1.39, respectively).(5) From 2004 to 2011, the rate of nonmedical use-related emergency room visits involving both opioids and benzodiazepines increased from 11 to 34.2 per 100,000 and drug overdose deaths involving both opioids and benzodiazepines increased from 0.6 to 1.7 per 100,000. The proportion of prescription opioid analgesic deaths which also involved benzodiazepines increased from 18% to 31% during this time.(6) A prospective observational cohort study in North Carolina found that the rates of overdose death among patients co-dispensed opioid analgesics and benzodiazepines were 10 times higher than patients receiving opioid analgesics alone.(7) A case-cohort study of VA data from 2004-2009 found that the risk of death from overdose increased with concomitant opioid analgesics and benzodiazepines. Compared to patients with no history of benzodiazepines, patients with a history of benzodiazepine use (hazard ratio [HR] = 2.33) and patients with a current benzodiazepine prescription (HR=3.86) had an increased risk of fatal overdose.(8) A study found that opioid analgesics contributed to 77% of deaths in which benzodiazepines were determined to be a cause of death and that benzodiazepines contributed to 30% of deaths in which opioid analgesics were determined to be a cause of death. This study also found that other CNS depressants (including barbiturates, antipsychotic and neuroleptic drugs, antiepileptic and antiparkinsonian drugs, anesthetics, autonomic nervous system drugs, and muscle relaxants) were contributory to death in many cases where opioid analgesics were also implicated.(9) A study found that alcohol was involved in 18.5% of opioid analgesic abuse-related ED visits and 22.1 percent of opioid analgesic-related deaths.(10)

Opioids (Immediate Release)/Sleep Drugs

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Concurrent use of opioids and sleep drugs may result in additive CNS depression and sleep-related disorders.(1)

CLINICAL EFFECTS: Concurrent use of opioids and other CNS depressants, such as sleep drugs, may result in profound sedation, respiratory depression, coma, and/or death.(1) Concurrent use of opioids with eszopiclone, zaleplon, or zolpidem may increase the risk of sleep-related disorders including central sleep apnea and sleep-related hypoxemia and complex sleep behaviors like sleepwalking, sleep driving, and other activities while not fully awake. Rarely, serious injuries or death have resulted from complex sleep behaviors.(2)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects.

PATIENT MANAGEMENT: Limit prescribing opioid analgesics with CNS depressants such as sleep drugs to patients for whom alternatives are ineffective, not tolerated, or would be otherwise inadequate to provide sufficient management of pain.(1) If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. If starting a CNS depressant (for an indication other than epilepsy) with an opioid analgesic, prescribe a lower initial dose of the CNS depressant than indicated in the absence of an opioid and titrate based upon clinical response. If an opioid analgesic is indicated in a patient already taking a CNS depressant, prescribe a lower dose of the opioid and titrate based upon clinical response.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(3) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Eszopiclone, zaleplon, and zolpidem are contraindicated in patients who have had a previous episode of complex sleep behavior.(2) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(4)

DISCUSSION: Between 2002 and 2014, the number of patients receiving an opioid analgesic increased 8%, from 75 million to 81 million patients, and the number of patients receiving a benzodiazepine increased 31%, from 23 million to 30 million patients. During this time, the proportion of patients receiving concurrent therapy increased 31%, from 23 million to 30 million patients.(5) From 2004 to 2011, the rate of nonmedical use-related emergency room visits involving both opioids and benzodiazepines increased from 11 to 34.2 per 100,000 and drug overdose deaths involving both opioids and benzodiazepines increased from 0.6 to 1.7 per 100,000. The proportion of prescription opioid analgesic deaths which also involved benzodiazepines increased from 18% to 31% during this time.(6) A prospective observational cohort study in North Carolina found that the rates of overdose death among patients co-dispensed opioid analgesics and benzodiazepines were 10 times higher than patients receiving opioid analgesics alone.(7) A case-cohort study of VA data from 2004-2009 found that the risk of death from overdose increased with concomitant opioid analgesics and benzodiazepines. Compared to patients with no history of benzodiazepines, patients with a history of benzodiazepine use (hazard ratio [HR] = 2.33) and patients with a current benzodiazepine prescription (HR=3.86) had an increased risk of fatal overdose.(8) A study found that opioid analgesics contributed to 77% of deaths in which benzodiazepines were determined to be a cause of death and that benzodiazepines contributed to 30% of deaths in which opioid analgesics were determined to be a cause of death. This study also found that other CNS depressants (including barbiturates, antipsychotic and neuroleptic drugs, antiepileptic and antiparkinsonian drugs, anesthetics, autonomic nervous system drugs, and muscle relaxants) were contributory to death in many cases where opioid analgesics were also implicated.(9) A study found that alcohol was involved in 18.5% of opioid analgesic abuse-related ED visits and 22.1 percent of opioid analgesic-related deaths.(10) As of April 2019, the FDA had identified 66 cases of complex sleep behaviors with eszopiclone, zaleplon, or zolpidem, of which 20 cases resulted in death and the remainder resulted in serious injuries. It was not reported how many of the cases involved concomitant use of other CNS depressants.(2)

Opioids (Ir & Er)/Gabapentinoids

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Opioid-induced reduction in GI motility may increase the absorption of gabapentin and pregabalin.(1) Gabapentin and pregabalin may reverse opioid-induced tolerance of respiratory depression.(2) Concurrent use may result in profound sedation, respiratory depression, coma, and/or death.(3)

CLINICAL EFFECTS: Concurrent use of opioids may result in elevated levels of and toxicity from gabapentin and pregabalin, including profound sedation, respiratory depression, coma, and/or death.(1-7)

PREDISPOSING FACTORS: Patients who are elderly, are taking other CNS depressants, have decreased renal function, and/or have conditions that reduce lung function (e.g. Chronic Obstructive Pulmonary Disease [COPD]) may be at a higher risk of this interaction.

PATIENT MANAGEMENT: Limit prescribing opioid analgesics and gabapentinoids to patients for whom alternatives are ineffective, not tolerated, or would be otherwise inadequate to provide sufficient management of pain.(1) If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. If starting a gabapentinoid with an opioid analgesic, prescribe a lower initial dose of the gabapentinoid than indicated in the absence of an opioid and titrate based upon clinical response. If an opioid analgesic is indicated in a patient already taking a gabapentinoid, prescribe a lower dose of the opioid and titrate based upon clinical response.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(8) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(9)

DISCUSSION: In a study in 12 healthy males, administration of a single dose of morphine (60 mg sustained release) increased the area-under-curve (AUC) of a single dose of gabapentin (600 mg) by 44%.(1,3,4) There were no affects on the pharmacokinetics of morphine.(1,3,4) The combination of gabapentin plus morphine increased pain tolerance over the combination of morphine plus placebo. Side effects were not significantly different between morphine plus placebo and morphine plus gabapentin.(1) A retrospective, case-control study of opioid users in Ontario, Canada between August 1, 1997 and December 31, 2013 who died of an opioid-related cause matched cases to up to 4 controls who also used opioids. Use of gabapentin in the 120 days prior to death resulted in a significant increase in odds of opioid-related death (OR 1.99, CI=1.61-2.47, p<0.001), compared to opioid use alone. Use of moderate dose (900 mg to 1,799 mg daily) or high dose (>= 1,800 mg daily) gabapentin increased the odds of opioid-related death 60% compared to opioid use without gabapentin. Review of gabapentin prescriptions from calendar year 2013 found that 46% of gabapentin users received at least 1 opioid prescription.(3) Among 49 case reports submitted to FDA over a 5 year period (2012-2017), 12 people died from respiratory depression with gabapentinoids. Two randomized, double-blind, placebo-controlled clinical trials in healthy people, three observational studies, and several studies in animals were reviewed. A trial showed that using pregabalin alone and using it with an opioid pain reliever can depress breathing function. Three observational studies showed a relationship between gabapentinoids given before surgery and respiratory depression occurring after surgery. Several animal studies also showed that pregabalin plus opioids can depress respiratory function.(7) A retrospective cohort study evaluated the risk of mortality among Medicare beneficiaries aged 65 and older who were taking gabapentin with or without concurrent use of opioids. All-cause mortality in gabapentin users compared to duloxetine users was 12.16 per 1,000 person years vs. 9.94 per 1,000 person years, respectively. Adjusted for covariates, the risk of all-cause mortality among gabapentin users on high-dose opioids was more than double the control group (hazard ratio (HR) 2.03, CI=1.19-3.46).(10)

Opioids/Buprenorphine; Pentazocine

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Buprenorphine is a partial agonist at mu-opiate receptors, exhibiting a ceiling effect at which higher doses produce no further effect. Pentazocine is a mixed agonist-antagonist at opiate receptors.(1) Full mu-opioid agonists (e.g., morphine, methadone) continue to have increased effects at higher doses without ceiling effects.(2)

CLINICAL EFFECTS: Concurrent use of buprenorphine or pentazocine with other opioids in opioid dependent patients may result in withdrawal symptoms. Concurrent use in other patients may result in additive or decreased analgesia and decreased opioid side effects.

PREDISPOSING FACTORS: Patients dependent on opioids or who take higher dosages of opioids may be more likely to experience withdrawal symptoms with concurrent use.

PATIENT MANAGEMENT: Use buprenorphine and pentazocine with caution in patients maintained or dependent on other opioids and monitor for signs of withdrawal. In other patients, also monitor for changes in analgesic effects. The manufacturer of Sublocade states buprenorphine may precipitate opioid withdrawal in patients who are currently physically dependent on full opioid agonists. The risk of withdrawal may be increased if buprenorphine is given less than 6 hours after short-acting opioids (such as heroin, morphine) and less than 24 hours after long-acting opioids (such as methadone).(3)

DISCUSSION: Concurrent use of buprenorphine with other opioids in opioid dependent patients could result in withdrawal symptoms. Concurrent use in other patients may result in additive or decreased analgesia, decreased opioid side effects, and/or renarcotization.(2) In clinical trials, administration of buprenorphine injection produced withdrawal symptoms in patients maintained on methadone (30 mg daily) when administered 2 hours post-methadone,(4) but not when administered 20 hours post-methadone.(5) In another study, sublingual buprenorphine produced withdrawal symptoms in patients maintained on methadone. Symptoms were more pronounced in patients maintained on 60 mg daily doses than in patients maintained on 30 mg daily doses.(6) In a study of 10 patients maintained on methadone (100 mg daily), only three were able to tolerate escalating sublingual doses of buprenorphine/naloxone up to 32/8 mg. Split doses produced less withdrawal symptoms than full doses.(7) In a case report, a heroin-user maintained in a buprenorphine-maintenance program began stockpiling his buprenorphine instead of ingesting it and began using heroin. He then decided to re-initiate treatment on his own and ingested between 80 and 88 mg of buprenorphine over a two day period and experienced extreme withdrawal symptoms, despite restarting heroin during these symptoms. Methadone relieved his withdrawal symptoms.(8)

Opioids/Butorphanol

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Butorphanol antagonize mu-opiate receptors. Other opioids agonize mu-opiate receptors.(1)

CLINICAL EFFECTS: Concurrent use of butorphanol with other opioids in opioid dependent patients may result in withdrawal symptoms. Concurrent use in other patients may result in additive or decreased analgesia and decreased opioid side effects.

PREDISPOSING FACTORS: Patients dependent on opioids may be more likely to experience withdrawal symptoms with concurrent use. Patients using higher doses of opioids may also be at a higher risk.

PATIENT MANAGEMENT: Use butorphanol with caution in patients maintained or dependent on other opioids and monitor for signs of withdrawal. In other patients, also monitor for changes in analgesic effects.

DISCUSSION: Because butorphanol antagonizes mu-opiate receptors and other opioids agonize mu-opiate receptors, concurrent use of buprenorphine with other opioids in opioid dependent patients may result in withdrawal symptoms. Concurrent use in other patients may result in additive or decreased analgesia and decreased opioid side effects.(1) In a study in patients maintained on methadone, butorphanol produced withdrawal symptoms comparable to naloxone.(2) In a case report, the use of remifentanil for conscious sedation in a patient maintained on butorphanol produced severe withdrawal symptoms.(3)

Opioids/Nalbuphine

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Nalbuphine(1) antagonizes mu-opiate receptors. Other opioids agonize mu-opiate receptors.

CLINICAL EFFECTS: Concurrent use of nalbuphine with other opioids in opioid dependent patients may result in withdrawal symptoms. Concurrent use in other patients may result in additive or decreased analgesia, decreased opioid side effects, and/or renarcotization.

PREDISPOSING FACTORS: Patients dependent on opioids may be more likely to experience withdrawal symptoms with concurrent use. In opioid naive patients, higher doses of nalbuphine may result in decreased analgesic effects.

PATIENT MANAGEMENT: Use nalbuphine with caution in patients maintained or dependent on other opioids and monitor for signs of withdrawal. In other patients, also monitor for changes in analgesic effects. If nalbuphine is used to reverse opioid anesthesia, monitor patients for renarcotization.

DISCUSSION: Nalbuphine has been successfully used as an adjunct to morphine without decreasing analgesic effects.(2,3) However, other studies reported increased morphine requirements in patients who had initially received nalbuphine.(4,5) Nalbuphine has been used to reverse fentanyl anesthesia;(8-13) however, patients often required additional pain medication(5-7) and some studies reported renarcotization after the effects of nalbuphine wore off.(9,10) Nalbuphine has also been used to prevent epidural fentanyl,(13) morphine(14-16), and hydromorphone induced pruritus;(17-18) however, one study reported shortening of the duration of analgesia(16) and another reported increased PCA demands.(17) In methadone-dependent subjects, administration of nalbuphine produced withdrawal symptoms similar to naloxone.(19,20) Administration of nalbuphine to patients maintained on controlled-release morphine resulted in withdrawal symptoms.(20,21)

Selected Opioid Analgesics/Cimetidine

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: The metabolism of selected opioid analgesics may be inhibited by cimetidine.(1-15) At doses of 800-2400 mg daily, cimetidine is a moderate inhibitor of CYP3A4 and a weak inhibitor of CYP1A2, CYP2C19, CYP2C9, and CYP2D6.(16) Benzhydrocodone is a prodrug of hydrocodone.(12)

CLINICAL EFFECTS: The effect of selected opioid analgesics may be increased including profound sedation, respiratory depression, coma, and/or death. Opioid analgesics have been associated with histamine release and is dependent on dose, route of administration, and rate of administration. Histamine release can cause arteriole dilation and contribute to a profound decrease in systemic blood pressure. The cardiovascular effects of histamine release occurring with the opioid analgesics may be decreased by giving cimetidine concurrently.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Cimetidine use at higher doses of 200-400 mg four times daily would have an increased risk of inhibiting the metabolism of opioid analgesics. Lower doses and over-the-counter doses of cimetidine would be expected to have a diminished effect. Consider using alternative H2 antagonists when long-term concurrent therapy with opioid analgesics is indicated. The manufacturer of sufentanil sublingual tablets states that if concomitant use with CYP3A4 inhibitors is necessary, consider use of an alternate agent that allows dose adjustment.(15) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(17) Monitor the patient for increased adverse effects of the opioid analgesic including respiratory and central nervous system depression, unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness. Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(18)

DISCUSSION: Severe respiratory depression has been reported with the concurrent administration of opioid analgesics and cimetidine. Systemic levels of opioid analgesics metabolized by CYP3A4 may be increased during concurrent use with cimetidine, a CYP3A4 inhibitor.(1-15) In a study of 6 healthy subjects, the effects of ketoconazole (a strong CYP3A4 inhibitor) 400 mg daily for 3 days on alfentanil were studied. The maximum concentration (Cmax) and area-under-curve (AUC) of alfentanil were increased with both sequential and simultaneous dosing of alfentanil with concurrent ketoconazole.(19) In a study of 16 healthy subjects, the effects of ketoconazole 300 mg twice daily for 2 days on fentanyl 5 mcg/kg single dose were examined. Fentanyl AUC was increased by 133% and clearance was reduced to 78%. The metabolism of fentanyl to norfentanyl by CYP3A4 was delayed and partial metabolic clearance decreased by 18% with concurrent ketoconazole.(20) In vitro results of the effects of ketoconazole on hydrocodone confirmed CYP3A4 is responsible for the metabolism of hydrocodone to norhydrocodone.(21) A review discussed the metabolism of hydrocodone by CYP2D6 to O-demethylated hydromorphone and by CYP3A4 to N-demethylated norhydrocodone. CYP3A4 activity is reported as higher in women resulting in higher fractions of the norhydrocodone metabolite in women than in men.(22) A case report of a 46 year old hemodialysis patient was on routine therapy with phenytoin 100 mg three times daily and cimetidine 300 mg three times daily. Four days after starting cimetidine, morphine 15 mg IM every 4 hours was initiated for pain. After the sixth dose of morphine, the patient was apneic with a respiratory rate of 3 breaths/minute and had a grand mal seizure. The patient responded to naloxone 0.4 mg IV single dose with improvement in respiratory rate to 12 breaths/minute. Cimetidine was stopped and phenytoin decreased to 100 mg twice daily with improvement after 80 hours from initial episode. A month later the patient required surgery and was given cimetidine 150 mg twice daily followed by Pantopon 15 mg IM every 3-6 hours postoperatively for pain. The patient again became apneic, confused, and developed muscle twitching which responded to naloxone 0.4 mg for 4 doses over the next 24 hours with complete recovery.(23) In a study of 8 healthy subjects, the effects of cimetidine on morphine were studied. Subjects were evaluated in three study periods: morphine 10 mg IM single dose; cimetidine 600 mg oral given one hour before morphine 10 mg IM single dose; and cimetidine 600 mg oral single dose. Morphine reduced resting ventilation and increased end-tidal CO2 with peak effects at 120 minutes and resolution at 12 hours. Morphine with cimetidine pretreatment had similar effects on resting ventilation and end-tidal CO2, however the recovery ratio from 120 to 720 minutes was significantly different than morphine alone (p<0.05).(24) In a study of 7 healthy subjects, the effects of cimetidine 300 mg oral four times daily for 4 days on morphine 10 mg IV single dose were evaluated. No significant differences were found in morphine concentrations at any time point from zero to ten hours after dose administration with and without cimetidine. Morphine elimination half-life (t1/2), systemic clearance, volume of distribution, and AUC with and without cimetidine had no statistical differences.(25) In a study of 40 patients undergoing elective coronary artery bypass graft surgery were randomized to receive either cimetidine 4 mg/kg, diphenhydramine 1 mg/kg, a combination of both cimetidine and diphenhydramine, or placebo, followed by morphine 1 mg/kg. Patients were randomized to one of four groups: 1. placebo plus morphine; 2. cimetidine plus morphine; 3. diphenhydramine plus morphine; or 4. cimetidine plus diphenhydramine plus morphine. Patients in group 1 had a 10-fold increase in plasma histamine levels within 2 minutes of morphine with a decrease in mean BP, diastolic BP, and systemic vascular resistance (SVR). Group 2 has similar effects with a peak change in SVR and plasma histamine rise within 2 minutes of morphine. The change in SVR was significant when compared to placebo but less than group 1. Group 3 patients had an increase in heart rate (HR) from diphenhydramine alone as well as peak effects within 2 minutes of morphine with decreases in BP and SVR but were less than morphine alone. Group 4 patients had a 7-fold increase in histamine with a significant increase in HR, diastolic BP, and BP. When group 4 is compared to group 1, patients had a decrease in SVR and diastolic BP that was significantly less despite comparable increases in plasma histamine.(26) In vitro testing of oxycodone and methadone, cimetidine caused a greater than 50% inhibition in all pathways: CYP2B6, CYP3A4, CYP2C18, and CYP2D6. Cimetidine was found to be a weak reversible inhibitor in vitro. Extrapolation of the data to in vivo inhibition is unlikely to produce significant inhibition unless concentrations exceed normal doses by 10-fold.(27) Two studies examined the effects of CYP2D6 and CYP3A4 on the metabolism of oxycodone as well as genetic polymorphism influences. After concurrent administration of oxycodone with ketoconazole, the Cmax of the metabolites noroxycodone and noroxymorphone were decreased by 80% from baseline.(28,29) A review discussed the metabolism of oxycodone by CYP3A4 to noroxycodone, the major metabolite with weak antinociceptive properties, and by CYP2D6 to the active minor metabolite oxymorphone.(30) In a study of 8 male subjects, effects of cimetidine 600 mg twice daily for seven days on pethidine 70 mg IV single dose was evaluated. Concurrent use with cimetidine was associated with a 22% decrease in clearance, 11% decrease in elimination rate, and a 13% decrease in volume of distribution of pethidine. Changes were also seen in norpethidine, the primary metabolite, with a 23% decrease in AUC and 29% decrease in Cmax.(31) Opioid analgesics linked to this monograph include: alfentanil, benzhydrocodone, dihydrocodeine, fentanyl, hydrocodone, meperidine, meptazinol, nalbuphine, oxycodone, oxymorphone, pentazocine, propoxyphene, and sufentanil.

Selected Opioids/Barbiturates; Phenobarbital; Primidone

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: There are two mechanisms involved in this interaction. Pharmacokinetic: alfentanil, benzhydrocodone, buprenorphine, fentanyl, hydrocodone, meperidine, oxycodone, and sufentanil are primarily metabolized by CYP3A4/5 and glucuronidation pathways.(1-8) Phenobarbital is an inducer of these pathways. Pharmacodynamic: both opioids and barbiturates are associated with respiratory depression; these effects may be additive.(1,3,9) Benzhydrocodone is a prodrug of hydrocodone.(2) Primidone is metabolized to phenobarbital.

CLINICAL EFFECTS: Short term or intermittent use of phenobarbital and opioids metabolized by CYP3A4 may be associated with respiratory suppression or other CNS depression. Continuous, longer term use of phenobarbital may result in decreased levels and effectiveness of the opioid. Induction of meperidine metabolism may result in an increase in levels of normeperidine, the toxic metabolite of meperidine, resulting in a higher risk of excitatory effects, including hallucinations, tremors, and seizures.(6,10)

PREDISPOSING FACTORS: Patients with a history of alcohol or sedative abuse may be at risk for relapse and overuse or abuse of prescribed phenobarbital.(1,3,5,11) Individuals with significant obstructive pulmonary disease, the elderly, and debilitated patients are at greater risk for respiratory depression from either agent.(1,3) Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks.

PATIENT MANAGEMENT: Patients on chronic therapy with phenobarbital who are newly starting opioids metabolized by CYP3A4 may need higher than usual doses of the opioid for analgesia or opioid maintenance.(1,3,12) Opioid-treated patients newly started on phenobarbital should be monitored initially for additive CNS sedation or respiratory depression, particularly when predisposing factors (e.g. COPD, sleep apnea, debilitation, elderly) are present. Continued use of phenobarbital leads to induction of the opioids' metabolism. The onset is gradual and may not peak for several weeks. Monitor patient for possible loss of efficacy or opioid withdrawal. If a patient has been maintained on concurrent treatment with an opioid metabolized by CYP3A4 and phenobarbital, and the phenobarbital is discontinued, opioid levels will gradually rise as induction effects diminish. Monitor for increased opioid effects and adjust the dose accordingly.(1,3,12) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(13) For patients receiving opioid maintenance treatment, it would be prudent to assure all controlled substance prescriptions are approved or written by the opioid provider. Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(14)

DISCUSSION: Alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, and sufentanil are metabolized by CYP3A4, and barbiturates, phenobarbital, and primidone would be expected to induce their metabolism.(1,2,4-6) Newer metabolites and minor metabolic pathways for buprenorphine have been recently described. Phenobarbital, an inducer of multiple enzyme pathways (e.g. CYP2B, CYP2C, CYP3A and UGT) could potentially lower systemic buprenorphine levels via major and minor pathways.(12)

Selected Opioids/Selected Moderate Cyp3a4 Inhibitors

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Inhibitors of CYP3A4 may inhibit the metabolism of alfentanil, benzhydrocodone, fentanyl,(1) hydrocodone, meperidine,(2) oxycodone,(3) and sufentanil.(4)

CLINICAL EFFECTS: The concurrent administration of a CYP3A4 inhibitor may result in elevated levels of and toxicity from alfentanil, benzhydrocodone, fentanyl,(1,5) hydrocodone, meperidine,(2) oxycodone(3) and sufentanil(4), including somnolence and potentially fatal respiratory depression.

PREDISPOSING FACTORS: Heat.

PATIENT MANAGEMENT: Monitor patients receiving moderate CYP3A4 inhibitors for an extended period of time. Dosage adjustments should be made if warranted. The manufacturer of sufentanil sublingual tablets states that if concomitant use with CYP3A4 inhibitors is necessary, consider use of an alternate agent that allows dose adjustment.(4) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(6) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(7) Avoid exposing the fentanyl patch application site and surrounding area to direct external heat sources as there have been reports of overdose and death as a result of exposure to heat.(1)

DISCUSSION: Fentanyl(1) and oxycodone(3) are metabolized by the CYP3A4 isoenzyme. Moderate and strong inhibitors of this isoenzyme are expected to increase fentanyl(1) and oxycodone(3) levels. In a single dose study of sufentanil sublingual tablet 15 mcg with a strong CYP3A4 inhibitor, ketoconazole, resulted in 77% and 19% greater AUC and Cmax values of sufentanil, respectively, compared to its administration alone.(4) In a randomized study in 30 patients, continuous diltiazem (1 mcg/kg/min) infusion had no effect on epidural fentanyl consumption when compared to placebo. There were no significant differences in Visual Analogue Scores (VAS), Verbal Rating Scores (VRS), or incidence of side effects, although there was a trend towards increased nausea with concurrent diltiazem.(5) In a randomized study of coronary artery bypass patients, concurrent diltiazem (60 mg orally 2 hours before induction of anesthesia then 0.1 mg/kg/hr infusion) increased the area-under-curve (AUC) and half-life of alfentanil by 40% and 50%, respectively, when compared to placebo. Patients who received diltiazem were extubated an average of 2.5 hours later than in patients who received placebo.(8) In a study in 13 patients, administration of a single dose of verapamil (75mcg/kg to 150mcg/kg) had no significant effects on the pharmacodynamic effects of a single dose of fentanyl; however, individual patients had modest decreases in blood pressure.(9) In a case report, concurrent diltiazem and fentanyl produced delirium.(10) A study in healthy subjects shown that the application of heat over the fentanyl patch system increased mean overall fentanyl exposure by 120% and average maximum fentanyl level by 61%.(1) Moderate inhibitors of CYP3A4 include: amprenavir, aprepitant, atazanavir, avacopan, berotralstat, clofazimine, conivaptan, darunavir, diltiazem, dronedarone, duvelisib, fedratinib, fosamprenavir, fosnetupitant, imatinib, isavuconazonium, lenacapavir, letermovir, netupitant, nilotinib, rilzabrutinib, schisandra, stiripentol, treosulfan, and verapamil.(11,12)

Selected Opioids/Selected Strong Cyp3a4 Inducers

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Strong inducers of CYP3A4 may induce the metabolism of alfentanil, benzhydrocodone, buprenorphine,(1) fentanyl, hydrocodone, meperidine,(2-4) morphine,(5) oxycodone, papaveretum, and sufentanil.(6)

CLINICAL EFFECTS: Concurrent use of a strong CYP3A4 inducer may result in decreased levels of alfentanil, benzhydrocodone, buprenorphine, fentanyl, hydrocodone, meperidine, morphine, oxycodone, papaveretum, and sufentanil, which may result in decreased effectiveness and may precipitate withdrawal symptoms.(1-6) Induction of meperidine metabolism may result in an increase in levels of normeperidine, the toxic metabolite of meperidine, resulting in a higher risk of excitatory effects, including hallucinations, tremors, and seizures.(2,3)

PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks.

PATIENT MANAGEMENT: Patients maintained on alfentanil, benzhydrocodone, buprenorphine, fentanyl, hydrocodone, meperidine, morphine, oxycodone, papaveretum, and sufentanil may require dosage adjustments if a strong CYP3A4 inducer is initiated or discontinued. The effects of the interaction may last for several weeks after the discontinuation of the inducer. Patients who transfer to Sublocade (extended release subcutaneous syringe buprenorphine) from transmucosal buprenorphine used concomitantly with CYP3A4 inducers should be monitored to ensure that the plasma buprenorphine level produced by Sublocade is adequate. If patients already on Sublocade require newly-initiated treatment with CYP3A4 inducer, the patient should be monitored for withdrawal. If the dose of Sublocade is not adequate in the absence of the concomitant medication, and the concomitant medication cannot be reduced or discontinued, the patient should be transitioned back to a formulation of buprenorphine that permits dose adjustment. If a patient has been stabilized on Sublocade with a CYP3A4 inducer and the concomitant medication is discontinued, the patient should be monitored for signs and symptoms of over-medication. Within 2 weeks of Sublocade administration, if the dose provided by Sublocade is excessive in the absence of the concomitant inducer, it may be necessary to remove the Sublocade and treat the patient with a formulation of buprenorphine that permits dose adjustments.(15) The manufacturer of sufentanil sublingual tablets states that if concomitant use with CYP3A4 inducers is necessary, consider use of an alternate agent that allows dose adjustment.(6)

DISCUSSION: In a study in 12 opoid-dependent patients, rifampin (600 mg daily) decreased the area-under-curve (AUC) of buprenorphine by 70%. Half of the subjects experienced withdrawal symptoms. When compared to historical values, there was no effect on rifampin levels.(1) In a study of four healthy volunteers, phenytoin increased meperidine clearance from 1017 +/- 225 ml/min (mean +/- SD) to 1280 +/- 130 ml/min and decreased half-life from 6.4 hours to 4.3 hours. Phenytoin also increased normeperidine AUC by 1.53-fold after IV meperidine and by 1.25-fold after oral meperidine.(3) In a study in 10 healthy subjects, pretreatment with rifampin (600 mg daily) for 13 days decreased the area-under-curve (AUC) and maximum concentration (Cmax) of a single dose of morphine by 28% and 41%, respectively. The AUCs of morphine-3-glucuronide and morphine-6-glucuronide were proportionally decreased as well. Following rifampin pretreatment, no analgesic effects of morphine were seen.(5) In a randomized controlled trial of 12 healthy participants St. John's wort decreased the oxycodone AUC by 50%, shortened the oxycodone elimination half-life, and decreased the self-reported drug effect of oxycodone compared to placebo.(7) In a study in 12 healthy subjects, pretreatment with rifampin had no effect on fentanyl Cmax or time to Cmax (Tmax) after administration of oral transmucosal fentanyl. However, fentanyl AUC decreased 62%.(8) In a study in 9 healthy subjects, rifampin increased the clearance of alfentanil by 169%. Alfentanil half-life decreased 61%.(9) In a study of patients undergoing craniotomy, higher fentanyl maintenance doses were required in patients receiving carbamazepine and phenytoin compared to control subjects not receiving enzyme-inducing agents.(10) There are case reports of decreased levels and effectiveness of oxycodone with concurrent phenytoin(11) and rifampin(12) and with concurrent fentanyl and rifampin.(13-14) Selected strong CYP3A4 inducers linked to this monograph include: apalutamide, carbamazepine, encorafenib, enzalutamide, fosphenytoin, ivosidenib, lumacaftor, mitotane, phenytoin, rifampin, rifapentine, and St. John's Wort.

Selected Serotonergic Opioids/Ziprasidone

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Concurrent use of serotonergic opioids such as meperidine or tramadol and antipsychotics such as ziprasidone may result in additive CNS depression or additive risk of serotonin syndrome.(1)

CLINICAL EFFECTS: Concurrent use of serotonergic opioids such as meperidine or tramadol and antipsychotics such as ziprasidone may result in profound sedation, respiratory depression, coma, and/or death.(1)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects. Serotonin syndrome risk is dose-related. Higher systemic concentrations of either drug would be predicted to increase risk for serotonin toxicity. Concomitant therapy with multiple agents which increase brain serotonin concentrations may also increase risk for serotonin syndrome.(2)

PATIENT MANAGEMENT: Limit prescribing opioid analgesics such as meperidine or tramadol with CNS depressants such as antipsychotics, including ziprasidone, to patients for whom alternatives are ineffective, not tolerated, or would be otherwise inadequate to provide sufficient management of pain.(1) If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. If starting a CNS depressant (for an indication other than epilepsy) with an opioid analgesic, prescribe a lower initial dose of the CNS depressant than indicated in the absence of an opioid and titrate based upon clinical response. If an opioid analgesic is indicated in a patient already taking a CNS depressant, prescribe a lower dose of the opioid and titrate based upon clinical response.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(2) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness,(1) as well as for signs of serotonin syndrome. Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(3)

DISCUSSION: A nested case-control study looked at the relationship between antipsychotic use and risk of acute respiratory failure. Current use of antipsychotics was associated with a 2.33-fold increase in risk of respiratory failure compared to no use of antipsychotics. The risk was also significantly increased in patients with recent use of antipsychotics (within the past 15-30 days, OR = 1.79) and recent past use (within 31-90 days OR = 1.41). The risk increased with higher doses and longer duration of use.(4) Between 2002 and 2014, the number of patients receiving an opioid analgesic increased 8%, from 75 million to 81 million patients, and the number of patients receiving a benzodiazepine increased 31%, from 23 million to 30 million patients. During this time, the proportion of patients receiving concurrent therapy increased 31%, from 23 million to 30 million patients.(5) From 2004 to 2011, the rate of nonmedical use-related emergency room visits involving both opioids and benzodiazepines increased from 11 to 34.2 per 100,000 and drug overdose deaths involving both opioids and benzodiazepines increased from 0.6 to 1.7 per 100,000. The proportion of prescription opioid analgesic deaths which also involved benzodiazepines increased from 18% to 31% during this time.(6) A prospective observational cohort study in North Carolina found that the rates of overdose death among patients co-dispensed opioid analgesics and benzodiazepines were 10 times higher than patients receiving opioid analgesics alone.(7) A case-cohort study of VA data from 2004-2009 found that the risk of death from overdose increased with concomitant opioid analgesics and benzodiazepines. Compared to patients with no history of benzodiazepines, patients with a history of benzodiazepine use (hazard ratio [HR] = 2.33) and patients with a current benzodiazepine prescription (HR=3.86) had an increased risk of fatal overdose.(8) A study found that opioid analgesics contributed to 77% of deaths in which benzodiazepines were determined to be a cause of death and that benzodiazepines contributed to 30% of deaths in which opioid analgesics were determined to be a cause of death. This study also found that other CNS depressants (including barbiturates, antipsychotic and neuroleptic drugs, antiepileptic and antiparkinsonian drugs, anesthetics, autonomic nervous system drugs, and muscle relaxants) were contributory to death in many cases where opioid analgesics were also implicated.(9) A study found that alcohol was involved in 18.5% of opioid analgesic abuse-related ED visits and 22.1 percent of opioid analgesic-related deaths.(10) Several cases of serotonin syndrome have been reported in patients receiving ziprasidone.(12-14)

Serotonergic Agents/Centanafadine

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Centanafadine is a norepinephrine, dopamine, and serotonin reuptake inhibitor.(1) Concurrent administration with one or more serotonergic agents may increase serotonin effects, resulting in serotonin toxicity.(1,2)

CLINICAL EFFECTS: Concurrent use of centanafadine with other serotonergic agents may increase the risk of serotonin syndrome, a potentially life-threatening syndrome which may include one or more of the following symptoms: tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(1,2)

PREDISPOSING FACTORS: Serotonin syndrome risk is dose-related. Higher systemic concentrations of either drug would be predicted to increase risk for serotonin toxicity.(2) Concomitant therapy with multiple agents which increase brain serotonin concentrations may also increase risk for serotonin syndrome.(2)

PATIENT MANAGEMENT: If concurrent use of centanafadine with other serotonergic agents is clinically warranted, counsel the patient on the increased risk of serotonin syndrome and monitor for symptoms. If symptoms of serotonin syndrome develop, discontinue centanafadine and/or the other serotonergic agents immediately and initiate supportive measures.(1)

DISCUSSION: Centanafadine inhibits reuptake of norepinephrine, dopamine, and serotonin.(1)

Serotonergic Agents/Gepirone

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Gepirone is a serotonin receptor agonist. Concurrent administration with one or more serotonergic agents may increase serotonin effects, resulting in serotonin toxicity.(1,2)

CLINICAL EFFECTS: Concurrent use of gepirone with other serotonergic agents may increase the risk of hypertensive crisis and serotonin syndrome, a potentially life-threatening syndrome which may include one or more of the following symptoms: tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(1)

PREDISPOSING FACTORS: Serotonin syndrome risk is dose-related. Higher systemic concentrations of either drug would be predicted to increase risk for serotonin toxicity.(2) Concomitant therapy with multiple agents which increase brain serotonin concentrations may also increase risk for serotonin syndrome.(2)

PATIENT MANAGEMENT: If concurrent use of gepirone with other serotonergic agents is clinically warranted, counsel the patient on the increased risk of serotonin syndrome and monitor for symptoms. If symptoms of serotonin syndrome develop, discontinue gepirone and/or the other serotonergic agents immediately and initiate supportive measures.(1)

DISCUSSION: Gepirone and its 3'-OH metabolite act as agonists at 5HT1A receptors. Use with other agents that also increase serotonin in the body must be undertaken with caution and monitored closely due to the risk of serotonin syndrome.(1)

There is no enhanced messaging for this drug.

• Acute asthma attack
• Serotonin syndrome

• Acute respiratory failure
• Adrenocortical insufficiency
• Alcohol intoxication
• Cor pulmonale
• Drug abuse
• Drug dependence
• Exacerbation of chronic obstructive pulmonary disease
• Familial dysautonomia
• Gastrointestinal obstruction
• History of opioid overdose
• Kidney disease with likely reduction in glomerular filtration rate (GFr)
• Kidney disease with reduction in glomerular filtration rate (GFr)
• Primary adrenocortical insufficiency
• Respiratory depression

• Atrial flutter
• Benign prostatic hyperplasia
• Hypotension
• Hypothyroidism
• Intracranial hypertension
• Myxedema
• Pheochromocytoma
• Seizure disorder
• Severe hepatic disease
• Sickle cell disease
• Supraventricular tachycardia
• Toxic psychosis
• Urethral stricture

There is no enhanced messaging for this drug.

More Frequent

• Flushing
• Hypotension

Less Frequent

• Acute cognitive impairment
• Atelectasis
• Bradycardia
• Bronchospastic pulmonary disease
• Dyspnea
• Involuntary muscle movement
• Laryngeal edema
• Laryngismus
• Orthostatic hypotension
• Respiratory depression
• Seizure disorder
• Tachycardia

Rare or Very Rare

• Accidental fall
• Acute respiratory failure
• Adrenocortical insufficiency
• Allergic dermatitis
• Anaphylaxis
• Androgen deficiency
• Cardiac arrest
• Drug dependence
• Hallucinations
• Pruritus of skin
• Serotonin syndrome
• Shock
• Skin rash
• Tonic clonic seizure
• Urticaria

More Frequent

• Constipation
• Dizziness
• Drowsy
• General weakness
• Nausea
• Sedation
• Syncope
• Vomiting

Less Frequent

• Agitation
• Biliary spasm
• Blurred vision
• Diplopia
• Dysphoric mood
• False sense of well-being
• Gastrointestinal irritation
• Headache disorder
• Hyperhidrosis
• Mood changes
• Nightmares
• Palpitations
• Ureteral spasm
• Urinary retention
• Visual changes
• Xerostomia

Rare or Very Rare

• Anticholinergic toxicity
• Delirium
• Dysphagia
• Erectile dysfunction
• Hypoglycemic disorder
• Infertility
• Libido changes
• Muscle fasciculation
• Non-cardiac chest pain
• Opioid induced allodynia
• Opioid induced hyperalgesia
• Phlebitis after infusion
• Tremor
• Vasodilation of blood vessels

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