Drug Interactions between bexarotene and Fasigyn

ADJUST DOSING INTERVAL: Food may enhance the oral bioavailability of bexarotene. In one clinical study, bexarotene peak plasma concentration (Cmax) and systemic exposure (AUC) resulting from a 75 to 300 mg dose were 35% and 48% higher, respectively, when administered after a fat-containing meal relative to a glucose solution. In all clinical trials, patients were instructed to take bexarotene with or immediately following a meal.

Coadministration with inhibitors of CYP450 3A4 such as grapefruit juice may theoretically increase the plasma concentrations of bexarotene. In vitro studies suggest that bexarotene is metabolized by CYP450 3A4. However, concomitant administration with multiple doses of ketoconazole, a potent CYP450 3A4 inhibitor, did not alter bexarotene plasma concentrations, which would imply that bexarotene elimination is not substantially dependent on CYP450 3A4 metabolism in vivo.

MANAGEMENT: Because safety and efficacy data are based upon administration with food, bexarotene should be administered once daily with a meal. Patients may want to avoid consuming large amounts of grapefruit or grapefruit juice.

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GENERALLY AVOID: Use of alcohol or products containing alcohol during nitroimidazole therapy may result in a disulfiram-like reaction in some patients. There have been a few case reports involving metronidazole, although data overall are not convincing. The presumed mechanism is inhibition of aldehyde dehydrogenase (ALDH) by metronidazole in a manner similar to disulfiram. Following ingestion of alcohol, inhibition of ALDH results in increased concentrations of acetaldehyde, the accumulation of which can produce an unpleasant physiologic response referred to as the 'disulfiram reaction'. Symptoms include flushing, throbbing in head and neck, throbbing headache, respiratory difficulty, nausea, vomiting, sweating, thirst, chest pain, palpitation, dyspnea, hyperventilation, tachycardia, hypotension, syncope, weakness, vertigo, blurred vision, and confusion. Severe reactions may result in respiratory depression, cardiovascular collapse, arrhythmia, myocardial infarction, acute congestive heart failure, unconsciousness, convulsions, and death. However, some investigators have questioned the disulfiram-like properties of metronidazole. One study found neither elevations in blood acetaldehyde nor objective or subjective signs of a disulfiram-like reaction to ethanol in six subjects treated with metronidazole (200 mg three times a day for 5 days) compared to six subjects who received placebo.

MANAGEMENT: Because clear evidence is lacking concerning the safety of ethanol use during nitroimidazole therapy, patients should be apprised of the potential for interaction and instructed to avoid alcoholic beverages and products containing alcohol or propylene glycol while using oral, intravenous, or vaginal preparations of a nitroimidazole. Alcoholic beverages should not be consumed for up to 3 days after completion of systemic nitroimidazole therapy.

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