Drug Interaction Report

ADJUST DOSE: Coadministration with bupropion may increase the plasma concentrations of drugs that are metabolized by CYP450 2D6 (e.g., selective serotonin reuptake inhibitors; tricyclic antidepressants; some beta blockers, antiarrhythmics, and antipsychotics). The mechanism is decreased clearance due to inhibition of CYP450 2D6 activity by bupropion. Approximately 93% of Caucasians and more than 98% of Asians and individuals of African descent are extensive metabolizers of CYP450 2D6 and may be affected by this interaction. In a study of 15 male volunteers who were extensive metabolizers of CYP450 2D6, administration of a single 50 mg dose of desipramine following treatment with bupropion 150 mg twice daily increased the desipramine peak plasma concentration (Cmax), systemic exposure (AUC) and half-life by an average of 2-, 5-, and 2-fold, respectively. The effect was present for at least 7 days after the last dose of bupropion. A case report describes a 4-fold increase in plasma levels of imipramine and its metabolite, desipramine, in a 64-year-old woman following the addition of bupropion 225 mg/day. Plasma levels of desipramine were increased twofold more than the imipramine levels, which is consistent with the fact that desipramine is primarily metabolized by CYP450 2D6 while imipramine is also metabolized by other CYP450 isoenzymes. In another report, an 83-year-old woman became unsteady, confused, and lethargic following the addition of bupropion SR 300 mg/day. Her nortriptyline level was found to have increased by 185%. A later rechallenge prompted recurrence of the interaction. Likewise, a 62-year-old woman with no history of seizures developed a generalized tonic-clonic seizure in association with toxic trimipramine plasma levels following the addition of bupropion 300 mg/day. No further seizures occurred following dosage reductions of both drugs.

MANAGEMENT: Caution is advised if bupropion must be used concomitantly with medications that undergo metabolism by CYP450 2D6, particularly those with a narrow therapeutic range. Concomitant medications should be initiated at the lower end of the dose range. Clinical and laboratory monitoring may be appropriate for some drugs whenever bupropion is added to or withdrawn from therapy.

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GENERALLY AVOID: Excessive use or abrupt discontinuation of alcohol after chronic ingestion may precipitate seizures in patients receiving bupropion. Additionally, there have been rare postmarketing reports of adverse neuropsychiatric events or reduced alcohol tolerance in patients who drank alcohol during treatment with bupropion. According to one forensic report, a patient died after taking large doses of both bupropion and alcohol. It is uncertain whether a drug interaction was involved. Single-dose studies in healthy volunteers given bupropion and alcohol failed to demonstrate either a significant pharmacokinetic or pharmacodynamic interaction.

MANAGEMENT: The manufacturer recommends that alcohol consumption be minimized or avoided during bupropion treatment. The use of bupropion is contraindicated in patients undergoing abrupt discontinuation of alcohol.

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GENERALLY AVOID: Alcohol may potentiate some of the pharmacologic effects of CNS-active agents. Use in combination may result in additive central nervous system depression and/or impairment of judgment, thinking, and psychomotor skills.

MANAGEMENT: Patients receiving CNS-active agents should be warned of this interaction and advised to avoid or limit consumption of alcohol. Ambulatory patients should be counseled to avoid hazardous activities requiring complete mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

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MONITOR: Additive or synergistic effects on blood pressure may occur when bupropion is combined with sympathomimetic agents such as nasal decongestants, adrenergic bronchodilators, ophthalmic vasoconstrictors, and systemic vasopressors. Treatment with bupropion can result in elevated blood pressure and hypertension. In clinical practice, hypertension, in some cases severe and requiring acute treatment, has been observed in patients receiving bupropion alone and in combination with nicotine replacement therapy. These events have occurred in both patients with and without evidence of preexisting hypertension. Furthermore, postmarketing cases of hypertensive crisis have been reported during the initial titration phase with bupropion-naltrexone treatment.

MANAGEMENT: Caution is advised when bupropion is used with other drugs that increase dopaminergic or noradrenergic activity due to an increased risk of hypertension. Blood pressure and heart rate should be measured prior to initiating bupropion therapy and monitored at regular intervals consistent with usual clinical practice, particularly in patients with preexisting hypertension. Dose reduction or discontinuation of bupropion should be considered in patients who experience clinically significant and sustained increases in blood pressure or heart rate.

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MONITOR: The concomitant use of bupropion and nicotine replacement for smoking cessation may increase the risk of hypertension. In a clinical study (n=250), 6.1% of patients who used sustained-release bupropion with nicotine transdermal system developed treatment-emergent hypertension, compared to 2.5% of patients treated with bupropion alone, 1.6% treated with nicotine alone, and 3.1% treated with placebo. Three patients in the bupropion plus nicotine group and one patient in the nicotine-only group discontinued treatment due to hypertension. The majority had evidence of preexisting hypertension.

MANAGEMENT: Blood pressure monitoring is recommended for patients concomitantly using bupropion and nicotine replacement for smoking cessation.

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