Clomipramine Hcl (clomipramine HCl)

Dosage of clomipramine hydrochloride is expressed in terms of the hydrochloride.

Because there is wide interindividual variation in dosage and dosage may differ in various disease states, the dosage of clomipramine hydrochloride must be individualized carefully.

Patients receiving clomipramine should be monitored for possible worsening of depression, suicidality, or unusual changes in behavior, especially at the beginning of therapy or during periods of dosage adjustment. (See Cautions: Precautions and Contraindications.)

The manufacturers and some clinicians recommend selecting an initial clomipramine dosage at the lower end of the recommended range since decreased hepatic, renal, or cardiac function and concomitant illness and medications are more frequent in geriatric patients.

Clomipramine hydrochloride is administered orally. The drug also has been administered IM+ or IV+, but a parenteral dosage form is not commercially available in the US.

During initial therapy when the dosage is being titrated, the manufacturers recommend that clomipramine be given in divided doses with meals to lessen adverse GI effects. After dosage titration, the total daily dose may be given once daily at bedtime to minimize adverse effects such as sedation during waking hours and enhance patient compliance.

Because of the similarity of clomipramine to other tricyclic antidepressants, all drug interactions that may occur with this class of drugs should be considered when clomipramine is used. (See Drug Interactions in the Tricyclic Antidepressants General Statement 28:16.04.28.) In addition, the possibility that clomipramine may interact with any concomitantly administered drug has not been evaluated systematically but should be considered.

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

Antidepressants/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: Sibutramine has demonstrated antidepressant effects. (1)

CLINICAL EFFECTS: Concurrent use of sibutramine and an antidepressant may result in additive or synergistic central nervous system (CNS) effects.

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 Australian,(2) Canadian,(1) and UK(3) manufacturers of sibutramine formerly stated that concurrent use with antidepressants is contraindicated. The Canadian manufacturer also states that concurrent use of St. John's wort is contraindicated.(1)

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. The use of sibutramine with other CNS-active agents has not been evaluated.(1-3)

Selected Antidepressants/Iomeprol

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: Both iomeprol and selected antidepressants may lower the seizure threshold.(1)

CLINICAL EFFECTS: Use of iomeprol in a patient receiving selected antidepressants may increase the risk of seizure.(1) Antidepressants included in this monograph are tricyclic antidepressants (except formulations which also include benzodiazepines), bupropion, and oral monoamine oxidase(MAO) inhibitors used to treat depression.

PREDISPOSING FACTORS: Iomeprol associated seizures are more likely in patients with intracranial tumors or epilepsy.(1)

PATIENT MANAGEMENT: The manufacturer of iomeprol states that tricyclic antidepressants and MAO inhibitors should be discontinued 48 hours before iomeprol use. Treatment with an antidepressant should not be resumed until 24 hours post-procedure.(1) The UK manufacturer of bupropion states that it must not be used in the presence of predisposing risk factors such as medicinals which are known to lower the seizure threshold unless there is a compelling clinical justification that concurrent use outweighs the potential increased risk of seizure.(2)

DISCUSSION: Because selected antidepressants may lower seizure threshold, antidepressants should be discontinued 48 hours before iomeprol use. Treatment with an antidepressant should not be resumed until 24 hours post-procedure.(1)

Selected Tricyclic Compounds/Lumefantrine

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: Lumefantrine may inhibit the metabolism of some tricyclic antidepressants by CYP2D6.(1,2)

CLINICAL EFFECTS: Concurrent administration of lumefantrine and some tricyclic antidepressants may result in elevated levels of the tricyclic antidepressants and toxicity.(1,2)

PREDISPOSING FACTORS: The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids). The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(3)

PATIENT MANAGEMENT: The UK manufacturer of artemether-lumefantrine states that the concurrent use of artemether-lumefantrine is contraindicated in patients receiving drugs that are metabolized by CYP2D6, such as some tricyclic antidepressants.(1) The US manufacturer of artemether-lumefantrine states that the concurrent use of artemether-lumefantrine should be avoided in patients receiving drugs that are metabolized by CYP2D6, such as some tricyclic antidepressants.(2)

DISCUSSION: Lumefantrine has been shown in vitro to inhibit CYP2D6. This may be clinically relevant for agents with a low therapeutic index that have cardiac effects.(1,2)

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.

Tricyclic & Tetracyclic Compounds/Cisapride

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: The concurrent use of cisapride with a tricyclic or tetracyclic compound may result in additive effects on the QT interval.(1,2)

CLINICAL EFFECTS: Concurrent use may result in prolongation of the QT interval, which may result in potentially life-threatening arrhythmias.(1,2)

PREDISPOSING FACTORS: The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(3) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(3)

PATIENT MANAGEMENT: The manufacturer of cisapride states that cisapride should not be concomitantly administered with agents known to prolong the QT interval such as certain tricyclic antidepressants and certain tetracyclic antidepressants.(1) The manufacturer of amitriptyline states under contraindications that amitriptyline should not be given with cisapride.(2) If concurrent therapy is deemed medically necessary, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting.

DISCUSSION: The manufacturer of cisapride states that QT prolongation, torsades de pointes (sometimes with syncope), cardiac arrest, and sudden death have been reported in patients who were not taking agents known to increase cisapride levels. Some of these patients were taking agents known to prolong the QT interval, such as certain tricyclic antidepressants and certain tetracyclic antidepressants. The manufacturer of cisapride states that cisapride should not be concomitantly administered with agents known to prolong the QT interval.(1) The manufacturer of amitriptyline states under contraindications that amitriptyline should not be given with cisapride due to the potential for increased QT interval and increased risk of arrhythmia.(2)

Tricyclic Compounds/Arbutamine

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: The exact mechanism of the interaction is unknown.

CLINICAL EFFECTS: The exact clinical effects are not stated.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The manufacturer of arbutamine states that arbutamine should not be administered with tricyclic antidepressants.(1)

DISCUSSION: The manufacturer of arbutamine states that arbutamine should not be administered with tricyclic antidepressants.(1) There is no published documentation for this interaction.

Tricyclic Compounds/Grepafloxacin; Sparfloxacin

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: Unknown. Possibly additive or synergistic effects on the QTc interval.

CLINICAL EFFECTS: Increased QTc intervals which may result in life-threatening arrhythmias such as torsades de pointes.

PREDISPOSING FACTORS: The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(3) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(3)

PATIENT MANAGEMENT: Concurrent administration of grepafloxacin and agents known to produce an increase in the QTc interval and/or torsades de pointes such as tricyclic antidepressants is contraindicated unless appropriate cardiac monitoring can be assured.(1) Concurrent administration of sparfloxacin and agents known to produce an increase in the QTc interval and/or torsades de pointes is contraindicated. The manufacturer of sparfloxacin states that concurrent administration of sparfloxacin and tricyclic antidepressants should be avoided.(2) If concurrent therapy is deemed medically necessary, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting.

DISCUSSION: There is no published documentation to support this potential drug interaction. The product information for grepafloxacin states that prolongation of the QTc interval has been observed in healthy subjects receiving grepafloxacin.(1) The product information for sparfloxacin states that torsades de pointes has been reported in patients receiving sparfloxacin and disopyramide and amiodarone. Therefore, concurrent administration of sparfloxacin and agents known to produce an increase in the QTc interval and/or torsades de pointes, such as tricyclic antidepressants, is contraindicated.(2)

Tricyclic Compounds/Halofantrine

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: Possibly additive effects on the QTc interval.

CLINICAL EFFECTS: Concurrent use of halofantrine and tricyclic antidepressants may pre-dispose patients to development of prolonged QTc intervals.(1)

PREDISPOSING FACTORS: The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(2) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(2)

PATIENT MANAGEMENT: The manufacturer of halofantrine states under the contraindications section of the prescribing information that unless there are compelling clinical reasons, halofantrine should not be used with tricyclic antidepressants.(1) If concurrent therapy is deemed medically necessary, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting.

DISCUSSION: There is no published documentation to support this potential interaction. Because concurrent use may pre-dispose patients to prolongation of the QTc interval, the manufacturer of halofantrine states under the contraindications section of the prescribing information that halofantrine should not be used with tricyclic antidepressants unless compelling clinical reasons exist.(1)

Tricyclic; Tetracyclic Compounds/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: Some MAO inhibitors may enhance the effects of tricyclic and tetracyclic compounds indirectly through inhibition of microsomal enzymes.(1) Tricyclic and tetracyclic compounds may sensitize post-synaptic receptors to amines that are accumulating extraneuronally as a result of MAO inhibition.(2) Similarity between cyclobenzaprine and TCAs warrants consideration of TCA interactions for cyclobenzaprine.(6) Mirtazapine, a tetracyclic antidepressant, should also be considered for this interaction.(7)

CLINICAL EFFECTS: Concurrent use may result in a severe reaction including hyperpyrexia, convulsions, excitability, fluctuations in blood pressure, convulsions, grand mal seizures, serotonin syndrome, coma, and death.(1,3-10) Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(11)

PREDISPOSING FACTORS: High doses of tricyclics or tetracyclics, or concurrent use of multiple drugs which increase CNS serotonin levels may increase risk for serotonin syndrome.

PATIENT MANAGEMENT: The concurrent use of tricyclic antidepressants, cyclobenzaprine or mirtazapine and MAO inhibitors is contraindicated by the manufacturers of tricyclic antidepressants, cyclobenzaprine, mirtazapine, and tranylcypromine.(1,3-10) The manufacturers of tricyclic antidepressants, cyclobenzaprine and mirtazapine recommend at least 14 days between switching therapies.(1,3-9) The manufacturer of tranylcypromine recommends a medication-free interval of at least a week when initiating tranylcypromine in patients who have previously received a tricyclic antidepressant, then initiating tranylcypromine at a reduced dosage of 50% for one week.(10) The US manufacturer of phenelzine states that at least 14 days should elapse between the discontinuation of phenelzine and the initiation of another antidepressant. If phenelzine is used concurrently with or within 10 days of another antidepressant, the patient should be cautioned regarding the possibility of an adverse drug interaction.(8) The US manufacturer of selegiline states that at least 14 days should elapse between the discontinuation of selegiline and the initiation of a tricyclic antidepressant.(9) In emergency situations in patients maintained on tricyclics or tetracyclics, weigh the availability and safety of alternatives to methylene blue against the risk of serotonin syndrome. If methylene blue therapy is required, the patient's tricyclic, cyclobenzaprine or tetracyclic should be immediately discontinued. Patients should be monitored for serotonin syndrome for 2 weeks or until 24 hours after the last dose of methylene blue, whichever comes first.(12) In non-emergency situations in patients maintained on tricyclics, cyclobenzaprine or tetracyclics when methylene blue therapy is planned, discontinue the patient's tricyclic or tetracyclic at least 2 weeks in advance of methylene blue therapy. The patient's tricyclic or tetracyclic therapy may be resumed 24 hours after the last dose of linezolid or methylene blue.(12) Do not initiate tricyclic, cyclobenzaprine or tetracyclic therapy in patients receiving methylene blue until 24 hours after the last dose of these agents.(12) 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: It should be noted that if this interaction occurs, the consequences will be immediate and severe. Effects may continue to be seen for several days after discontinuing the MAOI. The interaction has been reported with tricyclic antidepressants and selegiline.(9) Methylene blue, when administered intravenously, has been shown to reach sufficient concentrations to be a potent inhibitor of MAO-A.(14,15) Metaxalone is a weak inhibitor of MAO.(34,35) The FDA AERS contains reports of serotonin syndrome with concurrent injectable methylene blue and citalopram, clomipramine, escitalopram, desvenlafaxine, duloxetine, escitalopram, fluoxetine, fluvoxamine, paroxetine, sertraline, and venlafaxine. The risk of serotonin syndrome with other psychiatric drugs is unclear.(13) 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.

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

Agents That Affect Catecholamines/Iobenguane I 123

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

MECHANISM OF ACTION: Many compounds that reduce catecholamine uptake or that deplete catecholamine stores may interfere with iobenguane uptake into cells.(1)

CLINICAL EFFECTS: Compounds that reduce catecholamine uptake or that deplete catecholamine stores may interfere with imaging completed with iobenguane.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Discuss the use of agents that affect catecholamines. Discontinue drugs that reduce catecholamine uptake or deplete catecholamine stores prior to imaging with iobenguane. Before imaging with iobenguane, discontinue agents that affect catecholamines for at least 5 biological half-lives, as clinically tolerated.(1)

DISCUSSION: Many agents may reduce catecholamine uptake or deplete catecholamine stores.(1) Examples include: - CNS stimulants or amphetamines (e.g. cocaine, methylphenidate, dextroamphetamine) - norepinephrine and dopamine reuptake inhibitors (e.g. phentermine) - norepinephrine and serotonin reuptake inhibitors (e.g. tramadol) - monoamine oxidase inhibitors (e.g. phenelzine, linezolid) - central monoamine depleting drugs (e.g. reserpine) - non-select beta adrenergic blocking drugs (e.g. labetalol) - alpha agonists or alpha/beta agonists (e.g. pseudoephedrine, phenylephrine, ephedrine, phenylpropanolamine, naphazoline) - tricyclic antidepressants or norepinephrine reuptake inhibitors (e.g. amitriptyline, bupropion, duloxetine, mirtazapine, venlafaxine) - botanicals that may inhibit reuptake of norepinephrine, serotonin or dopamine (e.g. ephedra, ma huang, St. John's Wort, yohimbine)

Agents That Affect Catecholamines/Iobenguane I 131

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

MECHANISM OF ACTION: Many compounds that reduce catecholamine uptake or that deplete catecholamine stores may interfere with iobenguane uptake into cells.(1)

CLINICAL EFFECTS: Compounds that reduce catecholamine uptake or that deplete catecholamine stores may impact the dosimetry calculations or effectiveness of iobenguane.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Discuss the use of agents that affect catecholamines. Discontinue drugs that reduce catecholamine uptake or deplete catecholamine stores for at least 5 half-lives before administration of either the dosimetry or a therapeutic dose of iobenguane. Do not administer these drugs until at least 7 days after each iobenguane dose.(1)

DISCUSSION: Many agents may reduce catecholamine uptake or deplete catecholamine stores.(1) Examples include: - CNS stimulants or amphetamines (e.g. cocaine, methylphenidate, dextroamphetamine) - norepinephrine and dopamine reuptake inhibitors (e.g. phentermine) - norepinephrine and serotonin reuptake inhibitors (e.g. tramadol) - monoamine oxidase inhibitors (e.g. phenelzine, linezolid) - central monoamine depleting drugs (e.g. reserpine) - non-select beta adrenergic blocking drugs (e.g. labetalol) - alpha agonists or alpha/beta agonists (e.g. pseudoephedrine, phenylephrine, ephedrine, phenylpropanolamine, naphazoline) - tricyclic antidepressants or norepinephrine reuptake inhibitors (e.g. amitriptyline, bupropion, duloxetine, mirtazapine, venlafaxine) - botanicals that may inhibit reuptake of norepinephrine, serotonin or dopamine (e.g. ephedra, ma huang, St. John's Wort, yohimbine) - calcium channel blockers

Anticholinergics/Clozapine

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

MECHANISM OF ACTION: Clozapine has potent anticholinergic properties and inhibits serotonin receptors, including 5-HT3.(1-4) Both of these properties may cause inhibition of gastrointestinal (GI) smooth muscle contraction, resulting in decreased peristalsis.(3,4) These effects may be compounded by concurrent use of anticholinergic agents.(1-6)

CLINICAL EFFECTS: Concurrent use of clozapine with other anticholinergic agents may increase the risk of constipation (common) and serious bowel complications (uncommon), including complete bowel obstruction, fecal impaction, paralytic ileus and intestinal ischemia or infarction.(1-6)

PREDISPOSING FACTORS: The risk for serious bowel complications is higher with increasing age, higher frequency of constipation, and in patients on higher doses of clozapine or multiple anticholinergic agents.(1,5)

PATIENT MANAGEMENT: Avoid the use of other anticholinergic agents with clozapine.(1-6) 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.(2) Consider a prophylactic laxative in those with a history of constipation or bowel obstruction.(2) Review patient medication list for other anticholinergic agents. When possible, decrease the dosage or number of prescribed anticholinergic agents, particularly in the elderly. Counsel the patient about the importance of maintaining adequate hydration. Encourage regular exercise and eating a high-fiber diet.(2)

DISCUSSION: In a prospective cohort study of 26,720 schizophrenic patients in the Danish Central Psychiatric Research Registry, the odds ratio (OR) for ileus was 1.99 with clozapine and 1.48 with anticholinergics. The OR for fatal ileus was 6.73 with clozapine and 5.88 with anticholinergics. Use of anticholinergics with 1st generation antipsychotics (FGA) increased the risk of ileus compare to FGA alone, but this analysis was not done with clozapine.(5) A retrospective cohort study of 24,970 schizophrenic patients from the Taiwanese National Health Insurance Research Database found that the hazard ratio (HR) for clozapine-induced constipation increased from 1.64 when clozapine is used alone, to 2.15 when used concomitantly with anticholinergics. However, there was no significant difference in the HR for ileus when clozapine is used with and without anticholinergics (1.95 and 2.02, respectively).(6) In the French Pharmacovigilance Database, 7 of 38 cases of antipsychotic-associated ischemic colitis or intestinal necrosis involved clozapine, and 5 of these cases involved use of concomitant anticholinergic agents. Three patients died, one of whom was on concomitant anticholinergics.(3) In a case series, 4 of 9 cases of fatal clozapine-associated GI dysfunction involved concurrent anticholinergic agents.(4)

Anticholinergics/Glucagon (Diagnostic)

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

MECHANISM OF ACTION: Glucagon and anticholinergic agents may have additive effects on inhibition of gastrointestinal motility.(1)

CLINICAL EFFECTS: Concurrent use of glucagon with anticholinergic agents may increase the risk of gastrointestinal hypomotility, including constipation and bowel complications.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Concurrent use of glucagon as a diagnotic aid is not recommended with the use of anticholinergic agents.(1) If concurrent use is necessary, evaluate the patient's bowel function. Monitor for symptoms of constipation and gastrointestinal hypomotility.

DISCUSSION: Both glucagon and anticholinergic agents may have additive effects on inhibition of gastrointestinal motility and increase the risk of gastrointestinal adverse effects.(1)

Anticholinergics/Solid Oral Potassium Capsules

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

MECHANISM OF ACTION: Concentrated potassium may damage the lining of the GI tract. Anticholinergics delay gastric emptying, resulting in the potassium product remaining in the gastrointestinal tract for a longer period of time.(1-16))

CLINICAL EFFECTS: Use of solid oral dosage forms of potassium in patients treated with anticholinergics may result in gastrointestinal erosions, ulcers, stenosis and bleeding.(1-16)

PREDISPOSING FACTORS: Diseases or conditions which may increase risk for GI damage include: preexisting dysphagia, strictures, cardiomegaly, diabetic gastroparesis, elderly status, or insufficient oral intake to allow dilution of potassium.(1-10,21) Other drugs which may add to risk for GI damage include: nonsteroidal anti-inflammatory drugs (NSAIDs), bisphosphonates, or tetracyclines.(21)

PATIENT MANAGEMENT: Regulatory agency and manufacturer recommendations regarding this interaction: - In the US, all solid oral dosage forms (including tablets and extended release capsules) of potassium are contraindicated in patients receiving anticholinergics at sufficient dosages to result in systemic effects.(2-8) Patients receiving such anticholinergic therapy should use a liquid form of potassium chloride.(2) - In Canada, solid oral potassium is contraindicated in any patient with a cause for arrest or delay in tablet/capsule passage through the gastrointestinal tract and the manufacturers recommend caution with concurrent anticholinergic medications.(1,9-10) Evaluate each patient for predisposing factors which may increase risk for GI damage. In patients with multiple risk factors for harm, consider use of liquid potassium supplements, if tolerated. For patients receiving concomitant therapy, assure any potassium dose form is taken after meals with a large glass of water or other fluid. To decrease potassium concentration in the GI tract, limit each dose to 20 meq; if more than 20 meq daily is required, give in divided doses.(2) If concurrent therapy is warranted, monitor patients receiving concurrent therapy for signs of blood loss, including decreased hemoglobin, hematocrit, fecal occult blood, and/or decreased blood pressure and promptly evaluate patients with any symptoms. Patients should be instructed to immediately report any difficulty swallowing, abdominal pain, distention, severe vomiting, or gastrointestinal bleeding. Instruct patients to report any signs and symptoms of bleeding, such as unusual bleeding from the gums or nose; unusual bruising; red or black, tarry stools; red, pink or dark brown urine; acute abdominal or joint pain and/or swelling.

DISCUSSION: In clinical trials, there was a higher incidence of gastric and duodenal lesions in patients receiving a high dose of a wax-matrix controlled-release formulation with a concurrent anticholinergic agent. The lesions were asymptomatic and not accompanied by bleeding, as shown by a lack of positive Hemoccult tests.(1-17) Several studies suggest that the incidence of gastric and duodenal lesions may be less with the microencapsulated formulation of potassium chloride.(14-17)

Anticholinergics/Solid Oral Potassium Tablets

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

MECHANISM OF ACTION: Concentrated potassium may damage the lining of the GI tract. Anticholinergics delay gastric emptying, resulting in the potassium product remaining in the gastrointestinal tract for a longer period of time.(1-16)

CLINICAL EFFECTS: Use of solid oral dosage forms of potassium in patients treated with anticholinergics may result in gastrointestinal erosions, ulcers, stenosis and bleeding.(1-16)

PREDISPOSING FACTORS: Diseases or conditions which may increase risk for GI damage include: preexisting dysphagia, strictures, cardiomegaly, diabetic gastroparesis, elderly status, or insufficient oral intake to allow dilution of potassium.(1-10,21) Other drugs which may add to risk for GI damage include: nonsteroidal anti-inflammatory drugs (NSAIDs), bisphosphonates, or tetracyclines.(21)

PATIENT MANAGEMENT: Regulatory agency and manufacturer recommendations regarding this interaction: - In the US, all solid oral dosage forms (including tablets and extended release capsules) of potassium are contraindicated in patients receiving anticholinergics at sufficient dosages to result in systemic effects.(2-8) Patients receiving such anticholinergic therapy should use a liquid form of potassium chloride.(2) - In Canada, solid oral potassium is contraindicated in any patient with a cause for arrest or delay in tablet/capsule passage through the gastrointestinal tract and the manufacturers recommend caution with concurrent anticholinergic medications.(1,9-10) Evaluate each patient for predisposing factors which may increase risk for GI damage. In patients with multiple risk factors for harm, consider use of liquid potassium supplements, if tolerated. For patients receiving concomitant therapy, assure any potassium dose form is taken after meals with a large glass of water or other fluid. To decrease potassium concentration in the GI tract, limit each dose to 20 meq; if more than 20 meq daily is required, give in divided doses.(2) If concurrent therapy is warranted, monitor patients receiving concurrent therapy for signs of blood loss, including decreased hemoglobin, hematocrit, fecal occult blood, and/or decreased blood pressure and promptly evaluate patients with any symptoms. Patients should be instructed to immediately report any difficulty swallowing, abdominal pain, distention, severe vomiting, or gastrointestinal bleeding. Instruct patients to report any signs and symptoms of bleeding, such as unusual bleeding from the gums or nose; unusual bruising; red or black, tarry stools; red, pink or dark brown urine; acute abdominal or joint pain and/or swelling.

DISCUSSION: In clinical trials, there was a higher incidence of gastric and duodenal lesions in patients receiving a high dose of a wax-matrix controlled-release formulation with a concurrent anticholinergic agent. Some lesions were asymptomatic and not accompanied by bleeding, as shown by a lack of positive Hemoccult tests.(1-17) Several studies suggest that the incidence of gastric and duodenal lesions may be less with the microencapsulated formulation of potassium chloride.(14-17)

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)

Clomipramine; Imipramine; Ssris; Snris;/Meperidine

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)

Higher Strength Serotonergic Tcas/Fluoxetine;Paroxetine

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

MECHANISM OF ACTION: Depending upon the interacting combination, pharmacokinetic and/or pharmacodynamic interactions are possible. Fluoxetine is a moderate inhibitor of CYP2C19 and a strong inhibitor of CYP2D6.(1) Paroxetine is a strong inhibitor of CYP2D6.(1,2) Amitriptyline, clomipramine, and imipramine are metabolized by CYP2C19 and CYP2D6.(1) Fluoxetine, paroxetine, clomipramine, and imipramine significantly increase neuronal serotonin levels. Amitriptyline increases serotonin at higher dosages.

CLINICAL EFFECTS: Concurrent administration of fluoxetine or paroxetine with selected cyclic agents which are metabolized by CYP2D6 or CYP2C19 may result in an increase in serum levels, toxicities (e.g. risk for seizures, severe anticholinergic effects), and/or clinical effects of the tricyclic agent. Concurrent administration of fluoxetine or paroxetine with clomipramine, imipramine, and high dose amitriptyline may increase the risk for serotonin syndrome.

PREDISPOSING FACTORS: Higher doses or higher systemic concentrations of fluoxetine or paroxetine may increase the magnitude of this interaction. Concurrent use of multiple drugs which increase CNS serotonin levels would be expected to further increase risk for serotonin syndrome.(21) The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(4,5) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibitors its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(4,5) The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids). The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(6)

PATIENT MANAGEMENT: Patients should be observed for increased adverse effects and clinical effects of tricyclic compounds when concurrent therapy with fluoxetine or paroxetine is started or if the dosage of either agent is increased. Plasma concentrations of the tricyclic compound should be monitored and the dosage adjusted accordingly. If fluoxetine or paroxetine is discontinued in a patient receiving a tricyclic antidepressant, the dosage may need to be adjusted upward as the effects of enzyme inhibition wane. The effects of fluoxetine on hepatic metabolism may last for up to 5 weeks after fluoxetine discontinuation. A cyclic antidepressant started after the discontinuation of fluoxetine should be started at a lower initial dosage. Patients receiving fluoxetine or paroxetine and clomipramine, imipramine, or higher dose amitriptyline should be monitored for serotonin syndrome. Mild serotonin symptoms may include: shivering, diaphoresis, mydriasis, intermittent tremor, and/or myoclonus. Moderate serotonin symptoms may include: tachycardia, hypertension, hyperthermia, mydriasis, diaphoresis, hyperactive bowel sounds, hyperreflexia, and/OR clonus. Severe serotonin symptoms may include: severe hypertension and tachycardia, shock, agitated delirium, muscular rigidity, and/or hypertonicity. When concurrent therapy may be associated with QT prolongation, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, and fainting.

DISCUSSION: Case reports have shown that the addition of fluoxetine to a tricyclic compound therapy can result in an increase of 100-300% in the tricyclic compound plasma concentration as well as an increase in adverse effects, including seizures and delirium. In an 83 year-old patient, the combination of clomipramine and fluoxetine resulted in high clomipramine concentrations and cardiac side effects. In a 70 year old patient, the use of venlafaxine, fluoxetine, and nortriptyline was associated with severe anticholinergic side effects. This interaction was thought to be due to increased nortriptyline levels. QTc prolongation also exists with some antidepressants. In a case report, the combination of levofloxacin, imipramine, and fluoxetine was associated with a QTc of 509msec. The authors concluded that this interaction was due to the pharmacodynamic additive effect among fluoxetine, imipramine, and levofloxacin. Cyclic antidepressants included in this monograph are amitriptyline (> 40 mg), clomipramine (> 25 mg), and imipramine (> 10 mg).

Selected Tricyclic Antidepressants/Quinidine; Thioridazine

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

MECHANISM OF ACTION: Quinidine and thioridazine are strong inhibitors of CYP2D6.(1) Doses as low as 50 mg to 100 mg of thioridazine or 30 mg of quinidine will convert most individuals with a CYP2D6 extensive metabolizer (EM) genotype to a poor metabolizer (PM) phenotype.(2,3,7) CYP2D6 is the primary metabolic pathway for desipramine and nortriptyline; amitriptyline, clomipramine, doxepin, and imipramine are metabolized by both CYP2D6 and CYP2C19 pathways.

CLINICAL EFFECTS: Concurrent use of quinidine or thioridazine and selected tricyclic antidepressants (TCAs) may increase levels of the TCA and the risk for toxicities from either or both drugs. Risks include seizures, anticholinergic, sedative, and alpha-blocking effects.(1,3,4)

PREDISPOSING FACTORS: The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids). The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(8)

PATIENT MANAGEMENT: Alternative antipsychotics or antidepressants are available and should be used whenever possible due to the potential morbidity associated with this combination. If concomitant treatment is necessary, begin with a lower than usual TCA starting dose and closely monitor serum levels of the tricyclic antidepressant.(3,5) Dosages of desipramine above 40 mg daily with Nuedexta (dextromethorphan-quinidine) are not recommended.(6) If concurrent use with doxepin is warranted, monitor doxepin plasma concentrations and reduce the doxepin dose based on doxepin plasma concentrations.(9)

DISCUSSION: TCAs vary in their sensitivity to CYP2D6 inhibition: Paroxetine, another strong CYP2D6 inhibitor, increases the plasma concentration of amitriptyline by 60 percent. However, paroxetine is a more potent inhibitor for nortriptyline (active metabolite of amitriptyline) yielding a nortriptyline AUC ratio of 4.8. Desipramine is described as sensitive substrate at CYP2D6. Other strong CYP2D6 inhibitors, fluoxetine and paroxetine, increase desipramine AUC ratio by 7.8 and 5.4 respectively. Use of a combination product containing dextromethorphan-quinidine (30 mg/30 mg) increased steady state levels of desipramine (25 mg) by 8-fold.(6)

Tricyclic Compounds/Guanethidine; Guanadrel

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

MECHANISM OF ACTION: Uptake of guanethidine is blocked by tricyclic antidepressants at the adrenergic neuron.

CLINICAL EFFECTS: Concurrent use of tricyclic antidepressants may result in decreased guanethidine or guanadrel effectiveness. The effects may be seen for several days after discontinuation of the tricyclic antidepressant.

PREDISPOSING FACTORS: Possibly concurrent administration of drugs that inhibit hepatic enzymes.

PATIENT MANAGEMENT: Avoid concomitant administration of these drugs. If both drugs are administered, adjust the guanethidine dose as needed based on blood pressure.

DISCUSSION: This interaction is well documented. Similarity between cyclobenzaprine and TCA's warrants consideration of TCA interactions for cyclobenzaprine.

Tricyclic Compounds/Select Indirect-Acting Sympathomimetics

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

MECHANISM OF ACTION: Unknown. However, it is speculated that indirect-acting sympathomimetics would have decreased activity due to tricyclic blockage of their uptake into the adrenergic neuron.

CLINICAL EFFECTS: Decreased effect of indirect acting sympathomimetics.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Use of tricyclic compounds and indirect-acting sympathomimetics should be approached with caution. Monitor patients receiving concurrent therapy for decreased sympathomimetic efficacy.

DISCUSSION: The pressor effects of the indirect-acting sympathomimetic amines (e.g., amphetamines, ephedrine, and methylphenidate) are antagonized by tricyclic antidepressants.

Tricyclic Compounds/Select Mixed Acting Sympathomimetics

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

MECHANISM OF ACTION: Unknown. However, it is speculated that mixed acting sympathomimetics will show effects based on the predominance of either direct or indirect activity. Agents with predominate effects of direct-acting sympathomimetic amines are expected to have an enhanced effect due to tricyclic blockage of norepinephrine reuptake. Agents with predominate effects of indirect-acting sympathomimetics would have decreased activity due to tricyclic blockage of their uptake into the adrenergic neuron.

CLINICAL EFFECTS: Mixed acting sympathomimetics will show effects based on the predominance of either direct or indirect activity.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Consider avoiding the concurrent use of mixed-acting sympathomimetics and tricyclic compounds. If concurrent is warranted, the initial dose of the sympathomimetic should be lowered and the patient should be monitored for adverse cardiovascular effects.

DISCUSSION: Epinephrine and other direct-acting sympathomimetic amines exert enhanced cardiovascular effects (e.g., arrhythmias, hypertension, and tachycardia) in individuals concurrently receiving or previously treated with tricyclic antidepressants. Other direct and mixed acting sympathomimetic amines have also been reported to interact with tricyclic antidepressants. These include norepinephrine, phenylephrine, dopamine, and methoxamine. The pressor effects of the indirect-acting sympathomimetic amines (i.e., amphetamines, ephedrine, methylphenidate, pseudoephedrine, and tyramine) are antagonized by tricyclic antidepressants. Protriptyline, amitriptyline, and desipramine have also been reported to interact with direct-acting sympathomimetics.

Tricyclic Compounds/Selected Direct-Acting Sympathomimetics

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

MECHANISM OF ACTION: Unknown. However, it is speculated that direct-acting sympathomimetic amines have an enhanced effect due to tricyclic blockage of norepinephrine reuptake.

CLINICAL EFFECTS: Increased effect of direct acting sympathomimetics.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Consider avoiding the concurrent use of direct-acting sympathomimetics and tricyclic compounds. If concurrent use of direct-acting sympathomimetics and tricyclic compounds is warranted, the initial dose of the sympathomimetic should be lowered and the patient should be monitored for adverse cardiovascular effects. Use of tricyclic compounds and other sympathomimetics should be approached with caution.

DISCUSSION: Epinephrine and other direct-acting sympathomimetic amines exert enhanced cardiovascular effects (e.g., arrhythmias, hypertension, and tachycardia) in individuals concurrently receiving or previously treated with tricyclic antidepressants. Other direct and mixed acting sympathomimetic amines have also been reported to interact with tricyclic antidepressants. These include norepinephrine, phenylephrine, dopamine, and methoxamine. Protriptyline, amitriptyline, and desipramine have also been reported to interact with direct-acting sympathomimetics.

Tricyclic Compounds; Carbamazepine/Tapentadol

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

MECHANISM OF ACTION: Tapentadol and tricyclic compounds may lower the seizure threshold.(1) Tapentadol and tricyclic compounds may result in additive effects on serotonin levels.(1) Although not used therapeutically as an antidepressant, carbamazepine is a tricyclic compound.

CLINICAL EFFECTS: Concurrent use of tapentadol and a tricyclic compound may result in seizures or serotonin syndrome.(1)

PREDISPOSING FACTORS: Risk of seizures may be increased in patients with epilepsy, a history of seizures, head trauma, metabolic disorders, alcohol or drug withdrawal, or infections of the central nervous system.(1)

PATIENT MANAGEMENT: Tapentadol should be used with caution in patients taking tricyclic compounds, including carbamazepine. Monitor patients closely for serotonin syndrome.(1)

DISCUSSION: Concurrent use of tapentadol with tricyclic compounds may result in additive blockage of serotonin reuptake, leading to central serotonergic hyperstimulation. Cases of serotonin syndrome have been reported with tapentadol in combination with other serotonergic drugs.(1) Use of tapentadol has been associated with increased seizure frequency in patients with seizure disorders.(1)

Tricyclic Compounds; Carbamazepine/Tramadol

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

MECHANISM OF ACTION: Tramadol and tricyclic compounds may lower the seizure threshold.(1) Tramadol inhibits the reuptake of serotonin and norepinephrine but has weak opioid effects. M1, tramadol's active metabolite, is a stronger opioid and up to 6 times more potent than tramadol in producing analgesia.(1) Carbamazepine induces the metabolism of this tramadol opioid metabolite.

CLINICAL EFFECTS: Concurrent use of tramadol and a tricyclic compound may result in seizures or serotonin syndrome and may increase the risk of suicide.(1) Concurrent use of tramadol and carbamazepine may significantly reduce the analgesic effect of tramadol.(1) Although not used therapeutically as an antidepressant, carbamazepine is a tricyclic compound.

PREDISPOSING FACTORS: Risk of seizures may be increased in patients with epilepsy, a history of seizures, head trauma, metabolic disorders, alcohol or drug withdrawal, or infections of the central nervous system.(1)

PATIENT MANAGEMENT: Tramadol should be used with caution in patients taking tricyclic compounds.(1) The use of tramadol and carbamazepine is not recommended.(1) Carbamazepine induces metabolism (glucuronidation) of the tramadol opioid metabolite (M1). In patients on long-term carbamazepine when tramadol is started, achieving adequate analgesia may be difficult. Prescribing higher tramadol doses would be associated with higher parent drug levels which may result in serotonin and norepinephrine associated adverse effects. In patients receiving chronic tramadol treatment when carbamazepine is started, anticipate a reduction in analgesic effects. The maximal effects of carbamazepine on tramadol efficacy may not be seen for 2 or more weeks. Monitor for decreased tramadol efficacy, including symptoms of opioid withdrawal, after carbamazepine is initiated or when carbamazepine dosage is increased. If carbamazepine is to be discontinued in patients stabilized on the combination of tramadol and carbamazepine, gradually decrease the carbamazepine dose to decrease the risk of withdrawal seizures. As carbamazepine induction wanes, systemic tramadol metabolite concentrations will rise. The tramadol dose may need to be decreased to prevent tramadol toxicity.

DISCUSSION: The use of tramadol in patients treated with tricyclic compounds may increase the risk of seizures.(1) A review of 124 reports of seizures following tramadol therapy received by the FDA through July 31, 1996 revealed that 23% of the patients were also taking tricyclic antidepressants.(2) Therefore, the manufacturer of tramadol states that tramadol should be used with caution in patients treated with tricyclic compounds.(1) The manufacturer of tramadol also states that the use of tramadol with carbamazepine is not recommended.(1) In a case report, a 79 year-old female developed serotonin syndrome three days after the addition of tramadol to amitriptyline therapy. Over the next four days, her condition deteriorated and she died.(3)

Tricyclic; Tetracyclic Agents; Carbamazepine/Linezolid

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

MECHANISM OF ACTION: Linezolid is a weak, reversible inhibitor of monoamine oxidase.(1) Tricyclic and tetracyclic compounds may sensitize post-synaptic receptors to amines that are accumulating extraneuronally as a result of MAO inhibition.(2) Carbamazepine is structurally related to the tricyclic antidepressants.(3) Similarity between cyclobenzaprine and tricyclics warrants consideration of tricyclic interactions for cyclobenzaprine.(4) Mirtazapine, a tetracyclic antidepressant, should also be considered for this interaction.(5)

CLINICAL EFFECTS: Concurrent use with linezolid may result in a severe reaction including hyperpyrexia, convulsions, excitability, fluctuations in blood pressure, convulsions, grand mal seizures, serotonin syndrome, coma, and death.(1) Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(6)

PREDISPOSING FACTORS: High doses of tricyclics or tetracyclics, or concurrent use of multiple drugs which increase CNS serotonin levels may increase risk for serotonin syndrome.

PATIENT MANAGEMENT: The manufacturers of the tricyclic antidepressants, carbamazepine, cyclobenzaprine and mirtazapine state that coadministration with MAO inhibitors is contraindicated. Concurrent linezolid is specifically contraindicated by the manufacturers of clomipramine, desipramine, mirtazapine, nortriptyline, and trimipramine.(1,3-5,7-12) The manufacturer of linezolid does not contraindicate the use of serotonergic agents but states that they should not be coadministered unless clinically appropriate and the patient is closely monitored.(1) This recommendation is consistent with the 2011 FDA Drug Safety Communication on linezolid and serotonergic psychiatric medications.(13,14) In non-emergency situations in patients maintained on tricyclics or tetracyclics when linezolid therapy is planned, discontinue the patient's tricyclic or tetracyclic at least 2 weeks in advance of linezolid therapy. In emergency situations in patients maintained on tricyclics or tetracyclics, weigh the availability and safety of alternatives to linezolid against the risk of serotonin syndrome. If linezolid therapy is required, the patient's tricyclic or tetracyclic should be immediately discontinued. Patients should be monitored for serotonin syndrome for 2 weeks or until 24 hours after the last dose of linezolid, whichever comes first. The patient's tricyclic or tetracyclic therapy may be resumed 24 hours after the last dose of linezolid.(13) Clinical studies have found a low incidence of serotonin syndrome in patients on concomitant linezolid and serotonergic agents, ranging from 0.24% to 4%, depending on the quality and size of the study. While linezolid-associated serotonin syndrome is potentially serious and fatal, if treated early, it is quickly reversible with discontinuation of offending agents and supportive care. Therefore, 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.(15-20) 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: It should be noted that if this interaction occurs, the consequences will be immediate and severe. Effects may continue to be seen for several days after discontinuing linezolid. The FDA FAERS contains reports of serotonin syndrome with the concurrent use of linezolid and citalopram, desvenlafaxine, duloxetine, escitalopram, fluoxetine, fluvoxamine, paroxetine, sertraline, and venlafaxine. The risk of serotonin syndrome with other psychiatric drugs is unclear.(14)

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)

Amitriptyline; Clomipramine; Nortriptyline/Valproic Acid

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

MECHANISM OF ACTION: Valproic acid may inhibit the metabolism of amitriptyline, clomipramine, and nortriptyline.

CLINICAL EFFECTS: Concurrent use of valproic acid may result in elevated levels of and toxicity from amitriptyline, clomipramine, and nortriptyline.

PREDISPOSING FACTORS: The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids). The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(1)

PATIENT MANAGEMENT: Patients receiving concurrent therapy should be monitored for signs of toxicity. Monitor tricyclic levels carefully during initiation, titration, and discontinuation of valproic acid. The dosage of the tricyclic antidepressant may need to be adjusted.

DISCUSSION: In a study in 15 healthy subjects, pretreatment with divalproex sodium (500 mg every 12 hours for 9 doses) increased the area-under-curve (AUC) and maximum concentration (Cmax) of a single dose of amitriptyline (50 mg) by 31% and 17%, respectively. The AUC and Cmax of nortriptyline increased by 55% and 28%, respectively. The sum of amitriptyline and nortriptyline AUC and Cmax increased by 42% and 19%, respectively.(2) In a study in 20 subjects with depression receiving amitriptyline (125 mg daily), 10 subjects received valpromide (600 mg daily). Amitriptyline and nortriptyline levels increased 50% and 65%, respectively, in subjects receiving concurrent valpromide.(3) There are case reports of encephalopathy and myoclonus,(4) status epilepticus,(5) and increased clomipramine levels(6) have been reported following concurrent administration of valproic acid and clomipramine. In a case report, a patient previous maintained on desipramine and valproic acid developed elevated desipramine levels following the discontinuation of valproic acid.(7) Extrapyramidal symptoms(8) and increased nortriptyline levels(9) have been reported with concurrent nortriptyline and valproic acid.

Anticholinergics/Topiramate

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

MECHANISM OF ACTION: Topiramate can cause decreased sweating and elevated body temperature. Agents with anticholinergic activity can predispose patients to heat-related disorders.(1-2)

CLINICAL EFFECTS: Concurrent use of topiramate with agents with anticholinergic activity may increase the incidence of oligohidrosis and hyperthermia, especially in pediatric or adolescent patients.(1-2) Overheating and dehydration can lead to brain damage and death.

PREDISPOSING FACTORS: Pediatric and adolescent patients and patients with dehydration may be more likely to experience heat-related disorders.(1)

PATIENT MANAGEMENT: The manufacturer of topiramate states that caution should be used when topiramate is prescribed with other medicinal products that predispose to heat-related disorders, such as agents with anticholinergic activity (e.g. clomipramine, hydroxyzine, diphenhydramine, haloperidol, imipramine, and oxybutynin) concurrently with zonisamide.(1) Monitor for signs and symptoms of heat stroke: skin feels very hot with little or no sweating, confusion, muscle cramps, rapid heartbeat, or rapid breathing. Monitor for signs and symptoms of dehydration: dry mouth, urinating less than usual, dark-colored urine, dry skin, feeling tired, dizziness, or irritability. If signs or symptoms of dehydration, oligohidrosis, or elevated body temperature occur, discontinuation of zonisamide should be considered.

DISCUSSION: Case reports of decreased sweating and elevated temperature have been reported, especially in pediatric patients. Some cases resulted in heat stroke that required hospital treatment.(1) A 64-year old woman developed non-exertional hyperthemia while taking multiple psychiatric medications with topiramate.(2)

Anticholinergics/Zonisamide

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

MECHANISM OF ACTION: Zonisamide can cause decreased sweating and elevated body temperature. Agents with anticholinergic activity can predispose patients to heat-related disorders.(1-2)

CLINICAL EFFECTS: Concurrent use of zonisamide with agents with anticholinergic activity may increase the incidence of oligohidrosis and hyperthermia, especially in pediatric or adolescent patients.(1-2) Overheating and dehydration can lead to brain damage and death.

PREDISPOSING FACTORS: Pediatric and adolescent patients and patients with dehydration may be more likely to experience heat-related disorders.(1)

PATIENT MANAGEMENT: The UK and US manufacturers of zonisamide state that caution should be used in adults when zonisamide is prescribed with other medicinal products that predispose to heat-related disorders, such as agents with anticholinergic activity.(1-2) Pediatric and adolescent patients must not take anticholinergic agents (e.g. clomipramine, hydroxyzine, diphenhydramine, haloperidol, imipramine, and oxybutynin) concurrently with zonisamide.(1) Monitor for signs and symptoms of heat stroke: skin feels very hot with little or no sweating, confusion, muscle cramps, rapid heartbeat, or rapid breathing. Monitor for signs and symptoms of dehydration: dry mouth, urinating less than usual, dark-colored urine, dry skin, feeling tired, dizziness, or irritability. If signs or symptoms of dehydration, oligohidrosis, or elevated body temperature occur, discontinuation of zonisamide should be considered.

DISCUSSION: Case reports of decreased sweating and elevated temperature have been reported, especially in pediatric patients. Some cases resulted in heat stroke that required hospital treatment and resulted in death.(1)

Clomipramine/Selected Anticoagulants (Vitamin K Antagonists)

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

MECHANISM OF ACTION: Clomipramine inhibition of platelet serotonin may result in impaired platelet aggregation.(1) This effect may be additive or synergistic when combined with other agents which impair hemostasis.

CLINICAL EFFECTS: Concurrent use of selected anticoagulants and clomipramine may increase the risk for bleeding.

PREDISPOSING FACTORS: The risk for bleeding episodes may be greater in patients with disease-associated factors (e.g. thrombocytopenia). Drug associated risk factors include concurrent use of multiple drugs which inhibit anticoagulant/antiplatelet metabolism and/or have an inherent risk for bleeding (e.g. NSAIDs).

PATIENT MANAGEMENT: If concurrent therapy is warranted, monitor patients for signs of blood loss, including decreased hemoglobin and/or hematocrit, fecal occult blood, and/or decreased blood pressure and promptly evaluate patients with any symptoms. When applicable, perform agent-specific laboratory test (e.g. INR, aPTT) to monitor efficacy and safety of anticoagulation. Discontinue anticoagulation in patients with active pathologic bleeding. Instruct patients to report any signs and symptoms of bleeding, such as unusual bleeding from the gums or nose; unusual bruising; red or black, tarry stools; red, pink or dark brown urine; acute abdominal or joint pain and/or swelling. The time of highest risk for a coumarin-type drug interaction is when the precipitant drug is initiated or discontinued. Contact the prescriber before initiating, altering the dose, or discontinuing either drug.

DISCUSSION: Clomipramine is a potent inhibitor of platelet serotonin. In a study of clomipramine and fluoxetine effects on platelet and plasma 5-HT levels, clomipramine significantly reduced platelet 5-HT content to 8% and 19% and plasma 5-HT levels to 40% and 23% of their pretreatment values after 12 weeks, respectively.(1) In a review describing the bleeding risk with SRIs, warfarin was associated with an increased rate of hemorrhage among SRI users (adjusted relative risk = 1.41).(2) In a cohort study of patients taking warfarin in combination with an SSRI versus warfarin treatment alone, an analysis including first bleedings revealed a hazard ratio of 3.49 for bleeding during treatment with a combination of SSRI and warfarin compared with warfarin only.(3) A retrospective study of warfarin-treated patients prescribed or not prescribed an antidepressant showed that use of an SSRI with warfarin was significantly associated with increased risk of any bleed (overall risk (OR)=2.6), major bleeding (OR=4.4), and hospitalization secondary to bleeding (OR=7.0) as compared to those not taking an SSRI.(4) A population based study of patient outcomes in 176 primary intracerebral hemorrhage patients showed that 19 patients taking SSRI/SNRIs together with warfarin had an increased 30-day case fatality rate of 78.9% compared to warfarin alone (50.7%).(5) In a study of the Anticoagulation and Risk factors in Atrial fibrillation (ATRIA) cohort, hemorrhage rates were higher during periods of SSRI exposure compared with periods on no antidepressants (2.32 per 100 person-years vs 1.35 per 100 person-years). After adjusting for bleeding risk and time in INR range > 3, SSRI exposure was associated with an increased rate of hemorrhage compared with no antidepressants (adjusted relative risk = 1.41).(6) Increased bleeding risk has been found when patients receive 3 agents which can affect bleeding risk: an anticoagulant, SSRI and NSAID.(7) In a retrospective review of 5 years of data from the Pharmaco-Epidemiologic Prescription Database, hospitalizations for upper gastro-intestinal bleeding in antidepressant users were compared to those in non-antidepressant users. The risk of a bleed in a patient using an NSAID only based on an observed-expected ratio was 4.5 and in a patient using low-dose aspirin only was 2.5. Concurrent use of a SSRI with NSAIDs or low-dose aspirin increased the risk of bleeding to 12.2 and 5.2, respectively.(7) In another study, there were 16 cases of upper gastrointestinal bleeding in patients receiving concurrent therapy with SSRIs and NSAIDs. Adjusted relative risk of bleeding with NSAIDs, SSRIs, or both were 3.7, 2.6, or 15.6, respectively.(8)

Clomipramine; Imipramine/Selected Ssris; Selected Snris

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

MECHANISM OF ACTION: The combination of clomipramine or imipramine with the selective serotonin reuptake inhibitors or serotonin norepinephrine reuptake inhibitors may have additive effects on serotonin levels.

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.(1)

PREDISPOSING FACTORS: Use of multiple drugs which increase serotonin levels.(1)

PATIENT MANAGEMENT: Patients receiving concurrent therapy should be observed for signs of increased serotonergic side effects. 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.

DISCUSSION: The tricyclic antidepressants clomipramine and imipramine possess significant serotonin reuptake inhibition properties.(2) Concurrent or recent use of other serotoninergic agents can increase the risk of serotonin syndrome.(1,2)

Lower Strength Serotonergic Tricyclics/Fluoxetine;Paroxetine

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

MECHANISM OF ACTION: Depending upon the interacting combination, pharmacokinetic and/or pharmacodynamic interactions are possible. Fluoxetine is a moderate inhibitor of CYP2C19 and a strong inhibitor of CYP2D6.(1) Paroxetine is a strong inhibitor of CYP2D6.(1,2) Amitriptyline, clomipramine, and imipramine are metabolized by CYP2C19 and CYP2D6.(1) Cyclobenzaprine is metabolized by CYP1A2 and CYP3A4 and so a pharmacokinetic interaction is not expected.(3) Fluoxetine, paroxetine, clomipramine and imipramine significantly increase neuronal serotonin levels. Amitriptyline increases serotonin at higher dosages.

CLINICAL EFFECTS: Concurrent administration of fluoxetine or paroxetine with tricyclics metabolized by CYP2D6 or CYP2C19 may result in an increase in serum levels, toxicities (e.g. risk for seizures, severe anticholinergic effects), and/or clinical effects of the tricyclic. Concurrent administration of fluoxetine or paroxetine with clomipramine and perhaps with imipramine, cyclobenzaprine, or high dose amitriptyline may increase the risk for serotonin syndrome.

PREDISPOSING FACTORS: Higher doses or higher systemic concentrations of fluoxetine or paroxetine may increase the magnitude of this interaction. The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(4,5) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibitors its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(4,5) Concurrent use of multiple drugs which increase CNS serotonin levels would be expected to further increase risk for serotonin syndrome.(6) The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids). The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(7)

PATIENT MANAGEMENT: Patients should be observed for increased adverse effects and clinical effects of tricyclic compounds when concurrent therapy with fluoxetine or paroxetine is started or if the dosage of either agent is increased. Plasma concentrations of the tricyclic compound should be monitored and the dosage adjusted accordingly. If the fluoxetine or paroxetine is discontinued in a patient receiving a tricyclic compound other than cyclobenzaprine the dosage may need to be adjusted upward as the effects of enzyme inhibition wane. The effects of fluoxetine on hepatic metabolism may last for 3-5 weeks after fluoxetine discontinuation. A cyclic compound (other than cyclobenzaprine) started after the discontinuation of fluoxetine should be started at a lower initial dosage. Patients receiving fluoxetine or paroxetine and clomipramine, imipramine, higher dose amitriptyline, or cyclobenzaprine should be monitored for serotonin syndrome. Mild serotonin symptoms may include: shivering, diaphoresis, mydriasis, intermittent tremor, and/or myoclonus. Moderate serotonin symptoms may include: tachycardia, hypertension, hyperthermia, mydriasis, diaphoresis, hyperactive bowel sounds, hyperreflexia, and/OR clonus. Severe serotonin symptoms may include: severe hypertension and tachycardia, shock, agitated delirium, muscular rigidity, and/or hypertonicity.(20) When concurrent therapy may be associated with QT prolongation, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting.

DISCUSSION: Case reports have shown that the addition of fluoxetine to a tricyclic compound therapy can result in an increase of 100-300% in the tricyclic compound plasma concentration as well as an increase in adverse effects, including seizures and delirium. In a 83 year-old patient, the combination of clomipramine and fluoxetine resulted in high clomipramine concentrations and cardiac side effects. The manufacturer of cyclobenzaprine reports that serotonin syndrome has been reported when combined with other serotonergic agents.(3) QTc prolongation also exists with some antidepressants. In a case report, the combination of levofloxacin, imipramine, and fluoxetine was associated with a QTc of 509msec. The authors concluded that this interaction was due to the pharmacodynamic additive effect among fluoxetine, imipramine, and levofloxacin. Cyclic agents included in this monograph are amitriptyline (<=40mg), clomipramine (<=25mg), cyclobenzaprine (structurally similar to amitriptyline), and imipramine (<=10mg).

Select Serotonergic Agents/Fentanyl

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

MECHANISM OF ACTION: Although the exact mechanism is not known, fentanyl is thought to have mild serotonergic effects.(1,7) Concurrent administration with one or more potent serotonergic agents may increase serotonin effects, leading to toxicity.

CLINICAL EFFECTS: Concurrent use of serotonergic agents and fentanyl may result in serotonin syndrome. Symptoms of serotonin syndrome may include tremor, agitation, diaphoresis, hyperreflexia, clonus, tachycardia, hyperthermia, and muscle rigidity.(1)

PREDISPOSING FACTORS: Based upon case reports, high fentanyl doses in the perioperative period, concomitant use of multiple serotonergic agents, or a recent increase in dosage of either agent may be risk factors for this interaction.(2-6)

PATIENT MANAGEMENT: Most patients tolerate the combination of fentanyl with serotonin-increasing agents. Serotonin syndrome constitutes a range of toxicities from mild to life threatening.(1) Monitor patients on multiple serotonergic agents for symptoms of serotonin toxicity. 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: Health Canada recently reported 5 cases of serotonin syndrome associated with patients receiving fentanyl and at least one other serotonergic agent.(2) Additional cases have been reported in the medical literature.(3-6) Serotonin increasing agents linked to this monograph are: centanafadine, citalopram, clomipramine, desvenlafaxine, duloxetine, fluoxetine, imipramine, levomilnacipran, milnacipran, paroxetine, sertraline, venlafaxine, vilazodone and vortioxetine.

Selected Cyp2d6 Inhibitors/Metoprolol

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

MECHANISM OF ACTION: CYP2D6 inhibitors may inhibit the metabolism of metoprolol.(1,2)

CLINICAL EFFECTS: Concurrent use of CYP2D6 inhibitors may result in elevated levels of and toxicity from metoprolol.(1,2)

PREDISPOSING FACTORS: The interaction may be more severe in patients who are ultrarapid metabolizers of CYP2D6.(1,2)

PATIENT MANAGEMENT: Monitor patients receiving concurrent therapy with metoprolol and inhibitors of CYP2D6. The dosage of metoprolol may need to be adjusted.(1,2)

DISCUSSION: In an open-label, randomized, cross-over study in 12 healthy males, celecoxib (200 mg BID) increased the AUC of metoprolol (50 mg) by 64%. One subject experienced a 200% increase.(3) In a randomized, double-blind, cross-over study in 7 healthy subjects, hydroxychloroquine (400 mg) increased the AUC of a single dose of metoprolol by 65%.(4) In a study in 20 Chinese patients with chronic myelogenous leukemia, imatinib (400 mg BID) increased the AUC of metoprolol (100 mg single dose) by 23%. (5) In healthy subjects, ranolazine (750 mg twice daily) increased plasma levels of a single dose of metoprolol (100 mg) by 1.8-fold.(6) CYP2D6 inhibitors include: abiraterone, asunaprevir, berotralstat, bupropion, capivasertib, celecoxib, chloroquine, cinacalcet, citalopram, clomipramine, dacomitinib, diphenhydramine, dronabinol, duloxetine, eliglustat, escitalopram, fedratinib, fluoxetine, hydroxychloroquine, imatinib, levomepromazine, lorcaserin, moclobemide, osilodrostat, paroxetine, quinine, ranitidine, ranolazine, rolapitant, and sertraline.

Selected Sensitive Cyp2d6 Substrates/Mirabegron

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

MECHANISM OF ACTION: Mirabegron is considered a moderate inhibitor of CYP2D6. FDA defines a moderate inhibitor as a drug which increases the area-under-curve (AUC) of a sensitive substrate 2 to 5 fold.(1,2)

CLINICAL EFFECTS: Concurrent use of mirabegron may lead to increased serum levels and adverse effects of drugs sensitive to inhibition of the CYP2D6 pathway.(1) Agents linked to this monograph are: atomoxetine, clomipramine, desipramine, duloxetine, imipramine, metoprolol, nebivolol, nortriptyline and yohimbine.

PREDISPOSING FACTORS: With desipramine, clomipramine, imipramine and nortriptyline, the risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids). The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(3)

PATIENT MANAGEMENT: Mirabegron has a long half-life of approximately 50 hours so extended monitoring over 10 to 13 days may be required to evaluate the full effect of this interaction. The manufacturer of mirabegron recommends appropriate monitoring and dose adjustment if necessary for drugs with a narrow therapeutic index.(1) Weigh the risks versus benefits of mirabegron treatment for overactive bladder symptoms based upon the interacting medication and patient specific characteristics.

DISCUSSION: The manufacturer of mirabegron conducted interaction studies with two sensitive substrates of CYP2D6: desipramine and metoprolol.(1) Mirabegron 160 mg daily for 5 days increased the AUC of a single dose of metoprolol 100mg by 229%. Mirabegron 100 mg daily for 18 days increased the AUC of a single dose of desipramine by 241%.

Selected Serotonergic Agents/Dextromethorphan

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

MECHANISM OF ACTION: Dextromethorphan inhibits neuronal reuptake of serotonin. Concurrent administration with one or more serotonergic agents may increase serotonin effects, leading to serotonin toxicity.(1-11)

CLINICAL EFFECTS: The concurrent use of dextromethorphan with serotonergic agents may increase the risk for serotonin syndrome. Serotonin syndrome constitutes a range of toxicities from mild to life threatening.(3) Mild serotonin symptoms may include: shivering, diaphoresis, mydriasis, intermittent tremor, and/or myoclonus.(3) Moderate serotonin symptoms may include: tachycardia, hypertension, hyperthermia, mydriasis, diaphoresis, hyperactive bowel sounds, hyperreflexia, and/OR clonus.(3) Severe serotonin symptoms may include: severe hypertension and tachycardia, shock, agitated delirium, muscular rigidity, and/or hypertonicity.(3)

PREDISPOSING FACTORS: Concurrent use of additional drugs which increase CNS serotonin levels would be expected to further increase risk for serotonin syndrome.(1-11)

PATIENT MANAGEMENT: Monitor patients on multiple serotonergic agents for symptoms of serotonin toxicity. Patients in whom serotonin syndrome is suspected should receive immediate medical attention. If the interacting agents are prescribed by different providers, it would be prudent to assure that both are aware of concomitant therapy and monitoring the patient for serotonin toxicities. Advise patients not to exceed recommended dosages of dextromethorphan. 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: Dextromethorphan inhibits neuronal reuptake of serotonin and may potentially precipitate dose-dependant serotonin toxicity in conjunction with other serotonergic agents.(4,5) Serotonin syndrome has been reported in patients following the addition of dextromethorphan containing cough syrups to duloxetine,(6) escitalopram,(7) fluoxetine,(8,9) paroxetine,(10) and sertraline.(11) Selected serotonergic agents linked to this monograph include: centanafadine, citalopram, clomipramine, duloxetine, escitalopram, fluvoxamine, imipramine, levomilnacipran, milnacipran, sertraline, venlafaxine, vilazodone and vortioxetine.

Selected Tricyclic Antidepressants/Cyclobenzaprine

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

MECHANISM OF ACTION: Cyclobenzaprine and selected tricyclic antidepressants (TCAs), including amitriptyline, clomipramine, and imipramine, may act synergistically to increase blood pressure and evoke behavioral excitation.(1)

CLINICAL EFFECTS: Concurrent administration of cyclobenzaprine with amitriptyline, clomipramine, or imipramine 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, hepatic dysfunction and use of multiple agents which increase central serotonin levels. Chronic use of cyclobenzaprine or high doses of TCAs would also be expected to increase the risk for serotonin toxicity.(1)

PATIENT MANAGEMENT: The US manufacturer of cyclobenzaprine recommends limiting use to short term duration, no more than two to three weeks. Use alternative therapy whenever possible, particularly in patients with hepatic impairment.(1) Based on serotonin receptor affinity, clomipramine would be expected to have higher risk of serotonin syndrome than imipramine followed by amitriptyline. Amitriptyline at low doses would be expected to have the lowest risk of serotonin syndrome. Cyclobenzaprine is structurally similar to tricyclic antidepressants (TCAs) and may affect serotonin receptors synergistically.(2,3) 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 and TCAs may also occur based on serotonin activity of both agents.(2,3) 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.(4) 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.(4) 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.(5)

Selected Tricyclic Compounds/Desvenlafaxine; Venlafaxine

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

MECHANISM OF ACTION: Desvenlafaxine or venlafaxine may impair the oxidative hepatic metabolism of tricyclic compounds via CYP2D6.

CLINICAL EFFECTS: Concurrent administration of desvenlafaxine or venlafaxine with a tricyclic compound may result in an increase in serum levels, toxicities, and/or clinical effects of the tricyclic compound.

PREDISPOSING FACTORS: The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids). The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(5)

PATIENT MANAGEMENT: Patients should be observed for increased adverse effects and clinical effects of tricyclic compounds at the initiation of concurrent therapy with desvenlafaxine or venlafaxine. Plasma concentrations of the tricyclic compound should be monitored and the dosage adjusted accordingly. If desvenlafaxine or venlafaxine is discontinued in a patient receiving a tricyclic compound, the dosage of the tricyclic compound may need to be adjusted. The US manufacturer of desvenlafaxine recommends the dose of desipramine be reduced by up to one-half when administered with desvenlafaxine 400 mg.

DISCUSSION: In a 70 year old patient, the use of venlafaxine, fluoxetine, and nortriptyline was associated with severe anticholinergic side effects. This interaction was thought to be due to increased nortriptyline levels. A case report of anticholinergic toxic syndrome with venlafaxine and desipramine combination exist as well. Concomitant administration of desvenlafaxine 400 mg with a single 50 mg dose of desipramine resulted in an increase in the Cmax and AUC of desipramine by approximately 50% and 90%. The affinity of the different SSRIs, SNRIs, and tricyclics for CYP P-450 may vary.

Selected Tricyclic Compounds/Duloxetine; Fluvoxamine

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

MECHANISM OF ACTION: Duloxetine or fluvoxamine may impair the oxidative hepatic metabolism of tricyclic compounds.

CLINICAL EFFECTS: Concurrent administration of duloxetine or fluvoxamine with a tricyclic compound may result in an increase in serum levels, toxicities (e.g. torsades de pointes), and/or clinical effects of the tricyclic compound.

PREDISPOSING FACTORS: The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids). The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(9)

PATIENT MANAGEMENT: Patients should be observed for increased adverse effects and clinical effects of tricyclic compounds at the initiation of concurrent therapy with duloxetine or fluvoxamine. Plasma concentrations of the tricyclic compound should be monitored and the dosage adjusted accordingly. If duloxetine or fluvoxamine is discontinued in a patient receiving a tricyclic compound, the dosage of the tricyclic compound may need to be adjusted.

DISCUSSION: In a study, pretreatment with duloxetine (60 mg twice daily) increased the area-under-curve (AUC) of a single dose of desipramine (50 mg) by 3-fold. Fluvoxamine has been shown in an in vitro study to inhibit the metabolism of imipramine. Three case reports have shown increased serum levels of imipramine (32%, 198%, and 470% increases) and an increase in adverse effects (anticholinergic effects, confusion, and sedation) during concurrent administration with fluvoxamine. Two case reports of adverse effects (tonic-clonic seizure, tremors, dizziness, and confusion) and increased plasma desipramine levels (79% and 54% increases) with concurrent administration of fluvoxamine exist. Increased plasma levels of clomipramine (586%) and amitriptyline (100-150%) without signs of clinical toxicity were seen following the addition of fluvoxamine to a tricyclic compound therapy. The affinity of the different SSRIs, SNRIs, and tricyclics for CYP450 may vary.

Selected Tricyclic Compounds/Sertraline

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

MECHANISM OF ACTION: Sertraline may impair the oxidative hepatic metabolism of tricyclic compounds.

CLINICAL EFFECTS: Concurrent administration of sertraline with a tricyclic compound may result in an increase in serum levels, toxicities, and/or clinical effects of the tricyclic compound.

PREDISPOSING FACTORS: The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids). The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(8)

PATIENT MANAGEMENT: Patients should be observed for increased adverse effects and clinical effects of tricyclic compounds at the initiation of concurrent therapy with sertraline. Plasma concentrations of the tricyclic compound should be monitored and the dosage adjusted accordingly. If sertraline is discontinued in a patient receiving a tricyclic compound, the dosage of the tricyclic compound may need to be adjusted.

DISCUSSION: Sertraline has been shown to increase the maximum concentration (Cmax) and AUC of desipramine by 31% and 23%, respectively.(5) The affinity of the different SSRIs, SNRIs, and tricyclics for CYP P-450 may vary.

Selected Weak Cyp2d6 Inhibitors/Tamoxifen

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

MECHANISM OF ACTION: Inhibitors of CYP2D6 may inhibit the conversion of tamoxifen to endoxifen (an active metabolite of tamoxifen).(1-2) The role of endoxifen in tamoxifen's efficacy has been debated and may involve a minimum concentration level.(3-5)

CLINICAL EFFECTS: Concurrent use of inhibitors of CYP2D6 may decrease the effectiveness of tamoxifen in preventing breast cancer recurrence.

PREDISPOSING FACTORS: Concurrent use of weak CYP2D6 inhibitors in patients who are CYP2D6 intermediate metabolizers should be avoided. Patients who are CYP2D6 poor metabolizers lack CYP2D6 function and are not affected by CYP2D6 inhibition.

PATIENT MANAGEMENT: Although data on this interaction are conflicting, it may be prudent to use alternatives to CYP2D6 inhibitors when possible in patients taking tamoxifen. The US manufacturer of tamoxifen states that the impact on the efficacy of tamoxifen by strong CYP2D6 inhibitors is uncertain and makes no recommendation regarding coadministration with inhibitors of CYP2D6.(12) The manufacturer of paroxetine (a strong CYP2D6 inhibitor) states that alternative agents with little or no CYP2D6 inhibition should be considered.(13) The National Comprehensive Cancer Network's breast cancer guidelines advises caution when coadministering strong CYP2D6 inhibitors with tamoxifen.(14) NCCN states when prescribing a selective serotonin reuptake inhibitor (SSRI), it is reasonable to avoid SSRIs that are strong and moderate CYP2D6 inhibitors, particularly fluoxetine and paroxetine, if an appropriate alternative exists.(14) Cancer Care Ontario breast cancer guidelines state concurrent use of weak CYP2D6 inhibitors should be closely monitored.(15) The European Society of Medical Oncology (ESMO) clinical practice guidelines for early breast cancer states patients on tamoxifen should be advised to avoid concurrent use of strong and moderate CYP2D6 inhibitors. Consider alternatives to tamoxifen if CYP2D6 inhibitors cannot be replaced with alternative agents.(16) If concurrent therapy is warranted, the risks versus benefits should be discussed with the patient.

DISCUSSION: Some studies have suggested that administration of fluoxetine, paroxetine, and quinidine with tamoxifen or a CYP2D6 poor metabolizer phenotype may result in a decrease in the formation of endoxifen (an active metabolite of tamoxifen) and a shorter time to breast cancer recurrence.(1-2,9) A retrospective study of 630 breast cancer patients found an increasing risk of breast cancer mortality with increasing durations of coadministration of tamoxifen and paroxetine. In the adjusted analysis, absolute increases of 25%, 50%, and 75% in the proportion of time of overlapping use of tamoxifen with paroxetine was associated with 24%, 54%, and 91% increase in the risk of death from breast cancer, respectively.(18) The CYP2D6 genotype of the patient may have a role in the effects of this interaction. Patients with wild-type CYP2D6 genotype may be affected to a greater extent by this interaction. Patients with a variant CYP2D6 genotype may have lower baseline levels of endoxifen and may be affected to a lesser extent by this interaction.(6-10) In a retrospective review, 1,325 patients treated with tamoxifen for breast cancer were classified as being poor 2D6 metabolizers (lacking functional CYP2D6 enzymes), intermediate metabolizers (heterozygous alleles), or extensive metabolizers (possessing 2 functional alleles). After a mean follow-up period of 6.3 years, the recurrence rates were 14.9%, 20.9%, and 29.0%, in extensive metabolizers, intermediate metabolizers, and poor metabolizers, respectively.(11) In October of 2006, the Advisory Committee Pharmaceutical Science, Clinical Pharmacology Subcommittee of the US Food and Drug Administration recommended that the US tamoxifen labeling be updated to include information about the increased risk of breast cancer recurrence in poor CYP2D6 metabolizers (either by genotype or drug interaction).(19-20) The labeling changes were never made due to ongoing uncertainty about the effects of CYP2D6 genotypes on tamoxifen efficacy. In contrast to the above information, two studies have shown no relationship between CYP2D6 genotype and breast cancer outcome.(21-23) As well, a number of studies found no association between use of CYP2D6 inhibitors and/or antidepressants in patients on tamoxifen and breast cancer recurrence,(24-28) though the studies were limited by problematic selection of CYP2D6 inhibitors and short follow-up. Weak inhibitors of CYP2D6 include: alogliptin, artesunate, celecoxib, chloroquine, cimetidine, clobazam, clomipramine, cobicistat, delavirdine, diltiazem, dimenhydrinate, diphenhydramine, dronabinol, dupilumab, echinacea, enasidenib, fedratinib, felodipine, fluvoxamine, gefitinib, hydralazine, imatinib, labetalol, lorcaserin, nicardipine, osilodrostat, ranitidine, ritonavir, sarpogrelate, sertraline, verapamil and viloxazine.(29)

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)

Serotonergic Agents/Ziprasidone

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

MECHANISM OF ACTION: Ziprasidone is a 5-HT1A agonist and serotonin and norepinephrine reuptake inhibitor. Concurrent administration with one or more serotonergic agents may increase serotonin effects, resulting in serotonin toxicity.(1,2)

CLINICAL EFFECTS: Concurrent use of ziprasidone and other serotonergic agents may result in serotonin syndrome, a potentially life-threatening condition with symptoms including altered mental status, hypertension, restlessness, myoclonus, hyperthermia, hyperreflexia, diaphoresis, shivering, and tremor.(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: Caution patients about the risk of serotonin syndrome with the concomitant use of ziprasidone with other serotonergic drugs. Instruct patients to contact their healthcare provider, or report to the emergency room, should they experience signs or symptoms of serotonin syndrome.(1)

DISCUSSION: Several cases of serotonin syndrome have been reported in patients receiving ziprasidone.(4-6)

Tricyclic Antidepressants/Bupropion

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

MECHANISM OF ACTION: Depending upon the antidepressant, one or two mechanisms may be involved. Both bupropion and tricyclic antidepressants are known to lower the seizure threshold.(1,2) Bupropion, a strong inhibitor of CYP2D6, may increase systemic exposure (AUC, area-under-curve) to tricyclic antidepressants that are metabolized by this pathway. Antidepressants which are very sensitive to CYP2D6 inhibition are: desipramine, doxepin, and trimipramine. Antidepressants which are moderately sensitive to CYP2D6 inhibition are: amitriptyline, imipramine, maprotiline, and nortriptyline. Antidepressants which are metabolized by CYP2D6 but less susceptible to CYP2D6 inhibition includes clomipramine.(3)

CLINICAL EFFECTS: Concurrent use of bupropion and a tricyclic antidepressant may result in additive effects on the seizure threshold, increasing the risk of seizures.(1,2) Concurrent use may also increase levels of and side effects from antidepressants metabolized by CYP2D6, such as amitriptyline, clomipramine, imipramine, maprotiline, and nortriptyline.(3)

PREDISPOSING FACTORS: The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; a total daily dose of bupropion greater than 450 mg or single doses greater than 150 mg; rapid escalation of bupropion dosage; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids).(1,2) The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(4)

PATIENT MANAGEMENT: The concurrent use of bupropion and tricyclic antidepressants should be undertaken only with extreme caution and with low initial bupropion dosing and small gradual dosage increases.(1,2) Single doses should not exceed 150 mg.(1,2) The maximum daily dose of bupropion should not exceed 300 mg for smoking cessation(2) or 450 mg for depression.(1) If concurrent use of doxepin and bupropion is warranted, monitor doxepin plasma concentrations and reduce the doxepin dose based on doxepin plasma concentrations.(5)

DISCUSSION: Because of the risk of seizure from concurrent bupropion and other agents that lower seizure threshold, the manufacturer of bupropion states that the concurrent use of bupropion and antidepressants should be undertaken only with extreme caution and with low initial bupropion dosing and small gradual dosage increases.(1,2) In a study in 15 male subjects who were extensive metabolizers of CYP2D6, bupropion (150 mg twice daily) increased the maximum concentration (Cmax), area-under-curve (AUC), and half-life (T1/2) of a single dose of desipramine (50 mg) by 2-fold, 5-fold, and 2-fold, respectively.(1,2)

Tricyclic Antidepressants/St. John's Wort

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

MECHANISM OF ACTION: St. John's wort may induce the metabolism of tricyclic antidepressants (TCAs) by the CYP P-450 isoenzyme system.(1)

CLINICAL EFFECTS: The concurrent administration of TCAs and St. John's wort may result in decreased levels and clinical effects of the TCA.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Patients receiving both of these medications should be alerted to the possibility of decreased effects of the TCA.(1) Observe the patient for loss of the therapeutic effect of the TCA and consider monitoring TCA levels during concurrent therapy. The dosage of the TCA may need to be adjusted if St. John's wort is added to or discontinued from concurrent therapy. St. John's wort may need to be discontinued.

DISCUSSION: St. John's wort has been shown to decrease levels of indinavir in healthy subjects.(2) Because TCAs (amitriptyline, amoxapine, imipramine) are metabolized by the same metabolic pathway, the FDA recommends that patients taking tricyclic antidepressants be alerted to the possibility of a drug interaction resulting in decreased levels and/or effects of the TCA.(1) In a study in 12 subjects, the addition of St. John's wort (900 mg day) decreased the area-under-curve (AUC) of amitriptyline (75 mg twice daily) by 22%. The AUC of nortriptyline decreased 41%.(3)

Tricyclic Antidepressants; Mianserin/Carbamazepine;Phenobarb

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

MECHANISM OF ACTION: Carbamazepine and phenobarbital may induce the metabolism of tricyclic antidepressants (TCAs) and mianserin by the CYP P450 isoenzyme system.(1,2)

CLINICAL EFFECTS: The concurrent administration of TCAs or mianserin with carbamazepine or phenobarbital may result in decreased levels and clinical effects of the TCA or mianserin.(1,2)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Patients receiving both of these medications should be alerted to the possibility of decreased effects of the TCA or mianserin.(1,2) Observe the patient for loss of the therapeutic effect of the TCA or mianserin and consider monitoring TCA or mianserin levels during concurrent therapy.(3,4) Consider dose adjustment of the TCA or mianserin if carbamazepine or phenobarbital is added to or discontinued from concurrent therapy.(2,4)

DISCUSSION: A study of 22 psychiatric patients examined the effects of carbamazepine on serum levels of several antidepressants. Carbamazepine lowered amitriptyline levels by 60%, doxepin levels by 55%, and mianserin levels by 70%. The authors recommended carefully monitoring antidepressant drug levels when carbamazepine is coadministered.(3) A large retrospective study found that patients on carbamazepine with amitriptyline or nortriptyline had concentration/dose (C/D) ratios for the antidepressants that were about 50% lower than the C/D ratios for patients not on carbamazepine. The authors suggest that therapeutic drug monitoring is valuable for managing drug interactions.(4) In healthy volunteers, carbamazepine 200 mg twice daily for 28 days increased desipramine clearance by 31%.(6) In a study of 13 patients with depression, carbamazepine 400 mg per day decreased total imipramine levels by 39.5% and desipramine levels by 24.5% but levels of the pharmacologically active free drugs were not affected. The authors suggested that dose adjustment of imipramine may not be necessary.(7) A pharmacokinetic study found that carbamazepine 400 mg per daily for 4 weeks decreased plasma concentrations of mianserin by 34-45%. A doubling of the mianserin dose was proposed when coadministered with carbamazepine.(5)

Tricyclic Compounds/Cimetidine

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

MECHANISM OF ACTION: Cimetidine inhibits the hepatic metabolism of tricyclic antidepressants.

CLINICAL EFFECTS: The pharmacological and toxic effects of tricyclic antidepressants may be increased.

PREDISPOSING FACTORS: The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids). The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(9)

PATIENT MANAGEMENT: Observe the patient for an increased or decreased response to tricyclic antidepressant therapy if cimetidine is started or stopped. Adjust the dose of the tricyclic agent accordingly. This interaction can probably be avoided by administration of an H-2 receptor antagonist other than cimetidine (e.g., famotidine, nizatidine, ranitidine).

DISCUSSION: Both controlled studies and case reports have demonstrated that concurrent administration of tricyclic antidepressants and cimetidine can result in an increase in plasma tricyclic antidepressant concentrations. Adverse effects have been reported. Similarity between cyclobenzaprine and TCA's warrants consideration of TCA interactions for cyclobenzaprine.

Tricyclic Compounds/Fosamprenavir; Tipranavir

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

MECHANISM OF ACTION: Fosamprenavir and tipranavir may inhibit the metabolism of tricyclic compounds.(1,2)

CLINICAL EFFECTS: Concurrent use of fosamprenavir(1) or tipranavir(2) with tricyclic compounds may result in elevated levels of the tricyclic agents and serious and/or life-threatening effects.

PREDISPOSING FACTORS: The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids). The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(4)

PATIENT MANAGEMENT: The manufacturer of fosamprenavir(1) recommends caution with concurrent use of these agents with tricyclic compounds, along with concentration monitoring of the tricyclics. The manufacturer of tipranavir recommends dosage reduction and concentration monitoring of desipramine when coadministered with tipranavir/ritonavir.(2)

DISCUSSION: Amprenavir has been shown to be a potent inhibitor of CYP3A4.(1,3) Fosamprenavir is a prodrug of amprenavir.(1) Therefore, the manufacturer of amprenavir(3) and fosamprenavir(1) recommends caution with concurrent use of these agents with tricyclic compounds, along with concentration monitoring of the tricyclic compounds. No interaction studies have been performed on the combination of tipranavir-ritonavir and desipramine. Desipramine is a sensitive substrate of CYP2D6 while tipranavir-ritonavir is a moderate CYP2D6 inhibitor.(5,6) In one clinical study, six subjects were given 50 mg desipramine on three occasions: alone, after a 60 mg dose of fluoxetine (strong CYP2D6 inhibitor), and after eight daily 60 mg doses of fluoxetine. Fluoxetine significantly reduced oral clearance of desipramine by up to 10-fold and prolonged the half-life of desipramine by up to 4-fold.(7)

Tricyclic Compounds/Inhaled Direct-Acting Sympathomimetics

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

MECHANISM OF ACTION: Unknown. However, it is speculated that direct-acting sympathomimetic amines have an enhanced effect due to tricyclic blockage of norepinephrine reuptake.

CLINICAL EFFECTS: Increased effect of direct acting sympathomimetics.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The concurrent use of inhaled sympathomimetics and tricyclic compounds or the use of these agents within 14 days of each other should be approached with extreme caution.

DISCUSSION: Epinephrine and other direct-acting sympathomimetic amines exert enhanced cardiovascular effects (e.g., arrhythmias, hypertension, and tachycardia) in individuals concurrently receiving or previously treated with tricyclic antidepressants. Protriptyline, amitriptyline, and desipramine have also been reported to interact with direct-acting sympathomimetics. Similarity between cyclobenzaprine and the tricyclic antidepressants consideration of tricyclic antidepressant interactions for cyclobenzaprine.

Tricyclic Compounds/Inhaled Indirect-Acting Sympathomimetics

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

MECHANISM OF ACTION: Unknown. However, it is speculated that indirect-acting sympathomimetics would have decreased activity due to tricyclic blockage of their uptake into the adrenergic neuron.

CLINICAL EFFECTS: Decreased effect of indirect acting sympathomimetics.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The concurrent use of inhaled sympathomimetics and tricyclic compounds or the use of these agents within 14 days of each other should be approached with extreme caution.

DISCUSSION: Epinephrine and other direct-acting sympathomimetic amines exert enhanced cardiovascular effects (e.g., arrhythmias, hypertension, and tachycardia) in individuals concurrently receiving or previously treated with tricyclic antidepressants. Similarity between cyclobenzaprine and the tricyclic antidepressants warrants consideration of tricyclic antidepressant interactions for cyclobenzaprine.

Tricyclic Compounds/Inhaled Mixed-Acting Sympathomimetics

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

MECHANISM OF ACTION: Unknown. However, it is speculated that indirect-acting sympathomimetics would have decreased activity due to tricyclic blockage of their uptake into the adrenergic neuron.

CLINICAL EFFECTS: Decreased effect of indirect acting sympathomimetics.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The concurrent use of inhaled sympathomimetics and tricyclic compounds or the use of these agents within 14 days of each other should be approached with extreme caution.

DISCUSSION: Mixed acting sympathomimetic amines have also been reported to interact with tricyclic antidepressants. These include norepinephrine, phenylephrine, dopamine, and methoxamine. Similarity between cyclobenzaprine and the tricyclic antidepressants consideration of tricyclic antidepressant interactions for cyclobenzaprine.

Tricyclic Compounds/Terbinafine

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

MECHANISM OF ACTION: Terbinafine may inhibit the metabolism of tricyclic compounds by CYP2D6.(1-5)

CLINICAL EFFECTS: Concurrent use of terbinafine may result in elevated levels of and toxicity from the tricyclic agent.

PREDISPOSING FACTORS: The risk of seizures may be increased in patients with a history of head trauma or prior seizure; CNS tumor; severe hepatic cirrhosis; excessive use of alcohol or sedatives; addiction to opiates, cocaine, or stimulants; use of over-the-counter stimulants and anorectics; diabetics treated with oral hypoglycemics or insulin; or with concomitant medications known to lower seizure threshold (antipsychotics, theophylline, systemic steroids). The risk of anticholinergic toxicities including cognitive decline, delirium, falls and fractures is increased in geriatric patients using more than one medicine with anticholinergic properties.(6)

PATIENT MANAGEMENT: Monitor tricyclic levels in patients receiving concurrent therapy with terbinafine. The dose of the tricyclic agent may need to be adjusted if terbinafine is initiated or discontinued. The effect of terbinafine on tricyclics may last for up to four weeks after terbinafine discontinuation.

DISCUSSION: In a study in 12 healthy subjects, a single dose of desipramine (50 mg) was given alone, after 21 days of terbinafine (250 mg daily), and 2 and 4 weeks after discontinuation of terbinafine. Administration after 21 days of terbinafine therapy increased the area-under-curve (AUC) and maximum concentration (Cmax) of desipramine by 5-fold and 2-fold, respectively. The AUC and Cmax of desipramine were still elevated when desipramine was administered 4 weeks after the completion of terbinafine therapy.(1,2) There are case reports of toxicity during concurrent terbinafine and desipramine,(3) imipramine,(4) and nortriptyline.(5,7-8) In the UK manufacturer states that terbinafine decreased the clearance of desipramine by 82%.(9)

Tricyclic Compounds; Mirtazapine/Clonidine

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

MECHANISM OF ACTION: Clonidine decreases blood pressure via alpha-2 agonism.(1) Tricyclic compounds(2) and mirtazapine(3) antagonize alpha-2, which may result in a loss of effect of clonidine.

CLINICAL EFFECTS: The concurrent use of clonidine and tricyclic compounds(1,3,4-16) and mirtazapine(3,17) may result in decreased effectiveness of clonidine and hypertensive crisis.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: If possible, avoid concurrent use of clonidine with tricyclic compounds or mirtazapine. Consider using an alternative agent in patients maintained on clonidine. If concurrent administration is warranted, blood pressure should be carefully monitored, particularly in the first two weeks of therapy, when this interaction is most likely to occur. The dosage of clonidine may need to be adjusted or the tricyclic compound or mirtazapine may need to be discontinued.

DISCUSSION: This interaction has been reported in patients receiving amitriptyline,(6) clomipramine,(7,8) desipramine,(2,9-11) imipramine(12-16), and protriptyline.(11) In one patient, a hypertensive crisis resulted. Other patients experienced a decrease in blood pressure control. A controlled trial demonstrated a decrease in anti-hypertensive effect when desipramine was added to a clonidine regimen. This decrease in hypertensive-control may be overcome by increasing the dose of clonidine and monitoring blood pressure closely. Cyclobenzaprine is structurally related to the tricyclic antidepressants and, especially at higher dosages, has similar effects.(18) Therefore, it is prudent to consider cyclobenzaprine in this interaction. Hypertensive crisis has been reported during concurrent clonidine and mirtazapine therapy.(3,17) Mianserin(19,20) and maprotiline,(21) tetracyclic antidepressants, have been shown not to affect the antihypertensive effects of clonidine.

Tricyclic Compounds; Mirtazapine/Moxonidine

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

MECHANISM OF ACTION: Moxonidine decreases blood pressure via imidazoline-1 and alpha-2 receptor agonism.(1) Tricyclic compounds(2) and mirtazapine(3) antagonize alpha-2, which may result in a loss of effect of moxonidine.

CLINICAL EFFECTS: The concurrent use of moxonidine and tricyclic compounds and mirtazapine may result in decreased effectiveness of moxonidine and decreased blood pressure control.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Concurrent use of moxonidine with tricyclic compounds or mirtazapine is not recommended.(1) Consider using an alternative agent in patients maintained on moxonidine. If concurrent administration is necessary, blood pressure should be carefully monitored. The dosage of moxonidine may need to be adjusted or the tricyclic compound or mirtazapine may need to be discontinued.

DISCUSSION: Moxonidine is an imidazoline-1 and alpha-2 receptor agonist.(1) Since tricyclic antidepressants and mirtazapine may reduce the effectiveness of centrally acting antihypertensive agents, the concurrent use of moxonidine is not recommended. No studies have evaluated the current use of moxonidine with tricyclic antidepressants or mirtazapine. Loss of blood pressure control and hypertensive crisis have been reported with clonidine,(4-22) and a similar interaction may occur with moxonidine. The sedative effect of tricyclic antidepressants can be potentiated by moxonidine.

Weak Cyp2d6 Inhibitors/Eliglustat

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

MECHANISM OF ACTION: Weak inhibitors of CYP2D6 may inhibit the metabolism of eliglustat. If the patient is also taking an inhibitor of CYP3A4, eliglustat metabolism can be further inhibited.(1)

CLINICAL EFFECTS: Concurrent use of an agent that is a weak inhibitor of CYP2D6 may result in elevated levels of and clinical effects of eliglustat, including prolongation of the PR, QTc, and/or QRS intervals, which may result in life-threatening cardiac arrhythmias.(1)

PREDISPOSING FACTORS: If the patient is also taking an inhibitor of CYP3A4 and/or has hepatic impairment, eliglustat metabolism can be further inhibited.(1) The risk of QT prolongation or torsades de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsades de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age.(2) Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsades de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, genetic impairment in drug metabolism or elimination, and/or renal/hepatic dysfunction).(2)

PATIENT MANAGEMENT: The dosage of eliglustat with weak inhibitors of CYP2D6 in poor CYP2D6 metabolizers should be limited to 84 mg daily.(1) The dosage of eliglustat with weak inhibitors of CYP2D6 in extensive CYP2D6 metabolizers with mild (Child-Pugh Class A) hepatic impairment should be limited to 84 mg daily.(1) If concurrent therapy is warranted, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting.

DISCUSSION: Paroxetine (30 mg daily), a strong inhibitor of CYP2D6, increased eliglustat (84 mg BID) maximum concentration (Cmax) and area-under-curve (AUC) by 7-fold and 8.4-fold, respectively, in extensive metabolizers. Physiologically-based pharmacokinetic (PKPB) models suggested paroxetine would increase eliglustat Cmax and AUC by 2.1-fold and 2.3-fold, respectively, in intermediate metabolizers. PKPB models suggested ketoconazole may increase the Cmax and AUC of eliglustat (84 mg daily) by 4.3-fold and 6.2-fold, respectively, in poor metabolizers.(1) PKPB models suggested terbinafine, a moderate inhibitor of CYP2D6, would increase eliglustat Cmax and AUC by 3.8-fold and 4.5-fold, respectively, in extensive metabolizers and by 1.6-fold and 1.6-fold, respectively in intermediate metabolizers. PKPB models suggest that concurrent eliglustat (84 mg BID), paroxetine (a strong inhibitor of CYP2D6), and ketoconazole would increase eliglustat Cmax and AUC by 16.7-fold and 24.2-fold, respectively, in extensive metabolizers. In intermediate metabolizers, eliglustat Cmax and AUC would be expected to increase 7.5-fold and 9.8-fold, respectively.(1) PKPB models suggest that concurrent eliglustat (84 mg BID), terbinafine (a moderate inhibitor of CYP2D6), and ketoconazole would increase eliglustat Cmax and AUC by 10.2-fold and 13.6-fold, respectively, in extensive metabolizers. In intermediate metabolizers, eliglustat Cmax and AUC would be expected to increase 4.2-fold and 5-fold, respectively.(1) A single dose of rolapitant increased dextromethorphan, a CYP2D6 substrate, about 3-fold on days 8 and day 22 following administration. Dextromethorphan levels remained elevated by 2.3-fold on day 28 after single dose rolapitant. The inhibitory effects of rolapitant on CYP2D6 are expected to persist beyond 28 days.(5) Weak inhibitors of CYP2D6 include: alogliptin, artesunate, celecoxib, chloroquine, chlorpromazine, clobazam, clomipramine, desvenlafaxine, dimenhydrinate, diphenhydramine, dronabinol, dupilumab, echinacea, enasidenib, felodipine, gefitinib, hydralazine, hydroxychloroquine, lorcaserin, methadone, panobinostat, propafenone, sarpogrelate, sertraline, vemurafenib, and venlafaxine.(3,4)

There is no enhanced messaging for this drug.

• 30 day risk period post-myocardial infarction
• Serotonin syndrome

• Angle-closure glaucoma
• Atrioventricular conduction defect
• Bipolar disorder
• Orthostatic hypotension
• Risk of angle-closure glaucoma due to narrow angle of anterior chamber of eye
• Seizure disorder
• Suicidal ideation

• Alcohol use disorder
• Chronic kidney disease stage 4 (severe) GFR 15-29 ml/min
• CYp2d6 poor metabolizer
• Disease of liver
• Hyperthyroidism
• Neuroblastoma
• Pheochromocytoma
• Urinary retention

There is no enhanced messaging for this drug.

More Frequent

• Myoclonus

Less Frequent

• Abnormal hepatic function tests
• Abnormal sexual function
• Acute cognitive impairment
• Bradycardia
• Cardiac arrhythmia
• Dysuria
• Hallucinations
• Hypotension
• Nervousness
• Tremor

Rare or Very Rare

• Abnormal ECG
• Agranulocytosis
• Allergic dermatitis
• Alopecia
• Anemia
• Anticholinergic toxicity
• Delusional disorder
• DRESS syndrome
• Drug-induced psychosis
• Epididymitis
• Galactorrhea not associated with childbirth
• Gynecomastia
• Hypokalemia
• Hypomania
• Hyponatremia
• Hypothyroidism
• Kidney stone
• Leukopenia
• Manic disorder
• Oculogyric crisis
• Ovarian cyst
• Pancytopenia
• Paralytic ileus
• Paranoid disorder
• Pharyngeal edema
• Pruritus of skin
• Purpura
• Secondary angle-closure glaucoma
• Seizure disorder
• Serotonin syndrome
• SIADH syndrome
• Skin photosensitivity
• Skin rash
• Suicidal ideation
• Thrombocytopenic disorder
• Tinnitus
• Ventricular premature beats

More Frequent

• Anorexia
• Constipation
• Dizziness
• Drowsy
• Dysgeusia
• Dyspepsia
• Erectile dysfunction
• Fatigue
• Headache disorder
• Increased appetite
• Insomnia
• Nausea
• Visual changes
• Weight gain
• Xerostomia

Less Frequent

• Acute abdominal pain
• Diarrhea
• Disturbance in thinking
• Flatulence
• Flushing
• Heartburn
• Hyperhidrosis
• Irregular menstrual periods
• Memory impairment
• Myalgia
• Orthostatic hypotension
• Paresthesia
• Pharyngitis
• Rhinitis
• Symptoms of anxiety
• Tachycardia
• Vertigo
• Vomiting

Rare or Very Rare

• Accidental fall
• Dry eye
• Dysmenorrhea
• Fever
• Increased urinary frequency
• Menorrhagia
• Mydriasis
• Polyuria
• Sinusitis
• Urinary incontinence

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Teratogenic effects were not observed in rats and mice receiving clomipramine hydrochloride dosages up to 20 times the maximum human daily dosage. Slight, nonspecific fetotoxic effects were observed in the offspring of pregnant mice receiving 10 times the maximum human daily dosage. Slight, nonspecific embryotoxicity occurred in rats receiving 5-10 times the maximum human daily dosage.

There are no adequate and controlled studies using clomipramine in pregnant women, and the drug should be used during pregnancy only if the possible benefits justify the potential risk to the fetus. Women should be advised to notify their physician if they are or plan to become pregnant during clomipramine therapy. Neonates whose mothers had received clomipramine throughout pregnancy in dosages of 75-250 mg daily have exhibited withdrawal manifestations or adverse effects, including jitteriness, tremor, seizures, twitching, hypertonia, hypotonia, tachypnea, respiratory acidosis, cyanosis, feeding difficulties, hypothermia, lethargy, and diaphoresis. Phenobarbital has been recommended by some clinicians for the management of neurologic withdrawal symptoms. Abrupt discontinuance of clomipramine at 32 weeks of pregnancy resulted in premature birth of a neonate who developed seizures soon after delivery. Because of the risk of neonatal withdrawal, some clinicians state that clomipramine therapy particularly should be avoided during late pregnancy.

Clomipramine is distributed into milk. (See Pharmacokinetics: Distribution.) Adverse effects were absent in an infant who was breast-feeding from a woman who continued treatment with clomipramine at a dosage of 150 mg daily. However, because of the potential for adverse reactions, including concern about the potential for tricyclic antidepressants to affect development of the CNS of infants, a decision should be made whether to discontinue nursing or clomipramine, taking into account the importance of the drug to the woman. Women should be advised to notify their physician if they are breast-feeding.

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