Drug Interactions between clomipramine and sodium phenylbutyrate / taurursodiol

MONITOR: Limited data suggest that the administration of clomipramine with grapefruit juice or cranberry juice may significantly increase plasma drug concentrations of clomipramine. Clomipramine is initially demethylated by CYP450 1A2, 3A3 and 3A4 before undergoing further metabolism to 8-hydroxyclomipramine. The increase in clomipramine bioavailability may stem from inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. The precise mechanism by which cranberry juice exerts its effects is unknown, but may involve inhibition of CYP450 isoenzymes. This interaction has occasionally been exploited in attempts to improve symptomatic control of obsessive compulsive disorder.

MANAGEMENT: Patients receiving clomipramine therapy who ingest cranberry juice, grapefruits, or grapefruit juice should be monitored for adverse effects and undue fluctuations in plasma drug levels.

ADJUST DOSING INTERVAL: Coadministration with a high-fat meal may reduce the rate and extent of absorption of sodium phenylbutyrate. When a single 3 g-1 g dose of sodium phenylbutyrate-taurursodiol (sodium phenylbutyrate-ursodoxicoltaurine) was administered to healthy volunteers in the presence of a high-fat, high-calorie meal (approximately 800 to 1000 calories; 500 to 600 calories from fat, 250 calories from carbohydrate, 150 calories from protein), sodium phenylbutyrate peak plasma concentration (Cmax) decreased by 75% and systemic exposure (AUC) decreased by 55%. The Cmax for taurursodiol was not significantly affected, but AUC was increased by 46%. The clinical significance of these changes has not been established. In premarketing studies, patients were advised to take the drug before a meal.

MANAGEMENT: The prescribing information recommends administration of sodium phenylbutyrate-taurursodiol before a meal or snack, particularly in patients of low body weight (less than 70 kg).

GENERALLY AVOID: The combination of ethanol and a tricyclic antidepressant may result in additive impairment of motor skills, especially driving skills. Also, one study has suggested that clomipramine metabolism is significantly impaired for several weeks or more following discontinuation of chronic alcohol consumption.

MANAGEMENT: Patients should be warned of this interaction and advised to limit their ethanol intake while taking tricyclic antidepressants. Monitoring for TCA toxicity (CNS depression, excessive anticholinergic effects, hypotension, arrhythmias) is recommended during alcohol withdrawal.