Horizant (gabapentin enacarbil)

No dosing information is available for this tab.

Gabapentin and gabapentin enacarbil are administered orally.

If discontinuance of gabapentin or gabapentin enacarbil therapy is required, gradual tapering of the dosage generally is recommended to avoid manifestations of abrupt withdrawal. (See Dosage and Administration: Dosage, and also see Cautions: Precautions and Contraindications.)

Patients who are currently receiving or beginning therapy with gabapentin, gabapentin enacarbil, and/or any other anticonvulsant for any indication should be closely monitored for the emergence or worsening of depression, suicidal thoughts or behavior (suicidality), and/or any unusual changes in mood or behavior. (See Suicidality under Cautions: Nervous System Effects and see Cautions: Precautions and Contraindications.)

No dosing information is available for this tab.

There is no enhanced messaging for this drug.

There are no contraindication interactions for this drug.

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

Agents That May Cause Respiratory Depression/Sodium Oxybate

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

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

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

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

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

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

Gabapentinoids/Opioids (Cough & Cold)

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

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

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

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

PATIENT MANAGEMENT: Avoid prescribing opioid-including cough medications for patients taking CNS depressants.(8) If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. If starting a gabapentinoid with an opioid analgesic, prescribe a lower initial dose of the gabapentinoid than indicated in the absence of an opioid and titrate based upon clinical response. If an opioid analgesic is indicated in a patient already taking a gabapentinoid, prescribe a lower dose of the opioid and titrate based upon clinical response.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(9) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(9)

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

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

Gabapentin/Aluminum; Magnesium-Containing Compounds

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

MECHANISM OF ACTION: Aluminum or magnesium containing products may reduce the bioavailability of gabapentin.(1)

CLINICAL EFFECTS: Simultaneous administration of aluminum or magnesium containing products and gabapentin may result in decreased absorption of gabapentin by 20% and reduce its clinical effectiveness.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: If the use of both medications is unavoidable, it is recommended that gabapentin be taken at least 2 hours following the administration of aluminum or magnesium containing products.(1)

DISCUSSION: In 16 subjects, Maalox reduced the bioavailability of gabapentin by about 20%. The reduction was only 5% when gabapentin was administered 2 hours after the Maalox dose. It is for this reason that the manufacturer of gabapentin recommends that it be taken at least 2 hours after the administration of aluminum or magnesium containing products.(1)

Gabapentinoids/Benzodiazepines

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

MECHANISM OF ACTION: Concurrent use may result in profound sedation, respiratory depression, coma, and/or death.(1-3)

CLINICAL EFFECTS: Concurrent use of benzodiazepines may result in elevated levels of and toxicity from gabapentin and pregabalin, including profound sedation, respiratory depression, coma, and/or death.(1-3)

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

PATIENT MANAGEMENT: Limit prescribing benzodiazepines and gabapentinoids to patients for whom alternatives are ineffective, not tolerated, or would be otherwise inadequate to provide sufficient management of pain.(1) If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. If starting a gabapentinoid with an benzodiazepine, prescribe a lower initial dose of the gabapentinoid than indicated in the absence of an opioid and titrate based upon clinical response. If a benzodiazepine is indicated (other than an indication of epilepsy) in a patient already taking a gabapentinoid, prescribe a lower dose of the benzodiazepine and titrate based upon clinical response.(1) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1)

DISCUSSION: Clinical trials have shown no pharmacokinetic interaction between pregabalin (300 mg BID) and lorazepam (1 mg single dose).(2) Among 49 case reports submitted to FDA over a 5 year period (2012-2017), 12 people died from respiratory depression with gabapentinoids. Two randomized, double-blind, placebo-controlled clinical trials in healthy people, three observational studies, and several studies in animals were reviewed. A trial showed that using pregabalin alone and using it with an opioid pain reliever can depress breathing function. Three observational studies showed a relationship between gabapentinoids given before surgery and respiratory depression occurring after surgery. Several animal studies also showed that pregabalin plus opioids can depress respiratory function. Benzodiazepines are expected to have a similar effect when used with gabapentinoids.(1)

Gabapentinoids/Muscle Relaxants

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

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

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

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

PATIENT MANAGEMENT: Limit prescribing muscle relaxants and gabapentinoids to patients for whom alternatives are ineffective, not tolerated, or would be otherwise inadequate to provide sufficient management of pain.(1) If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. If starting a gabapentinoid with a muscle relaxant, prescribe a lower initial dose of the gabapentinoid than indicated in the absence of a muscle relaxant and titrate based upon clinical response. If a muscle relaxant is indicated in a patient already taking a gabapentinoid, prescribe a lower dose of the muscle relaxant and titrate based upon clinical response.(1) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1)

DISCUSSION: Clinical trials have shown no pharmacokinetic interaction between pregabalin and muscle relaxants.(2) Among 49 case reports submitted to FDA over a 5 year period (2012-2017), 12 people died from respiratory depression with gabapentinoids. Two randomized, double-blind, placebo-controlled clinical trials in healthy people, three observational studies, and several studies in animals were reviewed. A trial showed that using pregabalin alone and using it with an opioid pain reliever can depress breathing function. Three observational studies showed a relationship between gabapentinoids given before surgery and respiratory depression occurring after surgery. Several animal studies also showed that pregabalin plus opioids can depress respiratory function. Muscle relaxants are expected to have a similar effect when used with gabapentinoids.(1)

Gabapentinoids/Opioids (Ir & Er)

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

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

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

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

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

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

There is no enhanced messaging for this drug.

There are no contraindication contraindications for this drug.

• Chronic kidney disease stage 3A (moderate) GFR 45-59 ml/min
• Chronic kidney disease stage 3B (moderate) GFR 30-44 ml/min
• Chronic kidney disease stage 4 (severe) GFR 15-29 ml/min
• Chronic kidney disease stage 5 (failure) GFr<15 ml/min
• Chronic obstructive pulmonary disease
• Myasthenia gravis
• Respiratory depression
• Suicidal ideation

• Depression
• Kidney disease with likely reduction in glomerular filtration rate (GFr)

There is no enhanced messaging for this drug.

More Frequent

• Ataxia
• Nystagmus

Less Frequent

• Altered mental status
• Depression
• Dyspnea
• Hostility
• Memory impairment
• Mood changes

Rare or Very Rare

• Abnormal hepatic function tests
• Acute cognitive impairment
• Anaphylaxis
• Angioedema
• Bullous pemphigoid
• DRESS syndrome
• Drug dependence
• Eosinophilia
• Erythema multiforme
• Hypersensitivity drug reaction
• Hyponatremia
• Irritability
• Jaundice
• Lymphadenopathy
• Multiple organ failure
• Respiratory depression
• Rhabdomyolysis
• Stevens-johnson syndrome
• Suicidal ideation
• Syncope

More Frequent

• Dizziness
• Drowsy
• Fatigue
• Peripheral edema
• Sedation

Less Frequent

• Acute bacterial otitis media
• Back pain
• Blurred vision
• Constipation
• Cough
• Diarrhea
• Diplopia
• Dry throat
• Dysarthria
• General weakness
• Hyperkinesis
• Malaise
• Nausea
• Pharyngitis
• Toxic amblyopia
• Tremor
• Viral infection
• Vomiting
• Weight gain
• Xerostomia

Rare or Very Rare

• Accidental fall
• Agitation
• Anorexia
• Behavioral disorders
• Concentration difficulty
• Conjunctivitis
• Dyspepsia
• Erectile dysfunction
• Fever
• Gynecomastia
• Headache disorder
• Hyperglycemia
• Hyperhidrosis
• Increased creatine kinase level
• Insomnia
• Libido changes
• Pain
• Rhinitis
• Skin rash
• Symptoms of anxiety

No enhanced messaging available.

No enhanced messaging available.

Although there are no adequate and controlled studies to date in pregnant women, gabapentin and gabapentin enacarbil have been shown to cause developmental toxicity when administered to pregnant animals during the period of organogenesis at doses similar to or lower than those used clinically. Such effects include skeletal abnormalities, hydroureter and hydronephrosis, and increased embryofetal mortality. In addition, abnormal or decreased synaptic formation was observed in neonatal mice exposed to intraperitoneal injections of gabapentin during the first postnatal week (corresponding to the last trimester of pregnancy in humans); the clinical importance of these findings is not known.

Gabapentin and gabapentin enacarbil should be used during pregnancy only when the potential benefits justify the possible risks to the fetus. Women who become pregnant while receiving gabapentin should be encouraged to enroll in the North American Antiepileptic Drug (NAAED) Pregnancy Registry by calling 888-233-2334; registry information also is available on the website at https://www.aedpregnancyregistry.org.

Gabapentin is distributed into milk following oral administration. Because of the potential for serious adverse reactions to gabapentin in nursing infants, the drug should be administered to nursing women only if the potential benefits justify the risk to the infant. The manufacturer of gabapentin enacarbil states that a decision should be made whether to discontinue nursing or the drug, taking into account the importance of the drug to the woman.

No enhanced messaging available.