Drug Interaction Report

MONITOR: Coadministration with inducers of CYP450 3A4 may decrease the plasma concentrations of rolapitant, which is primarily metabolized by the isoenzyme. When the potent CYP450 3A4 inducer rifampin was administered at 600 mg once daily for 7 days before and 7 days after a single 180 mg dose of rolapitant, mean rolapitant peak plasma concentration (Cmax) and systemic exposure decreased by 30% and 85%, respectively, compared to administration of rolapitant alone. Mean half-life of rolapitant decreased from 176 hours to 41 hours with rifampin. No data are available for other, less potent CYP450 3A4 inducers.

MANAGEMENT: The potential for diminished pharmacologic effects of rolapitant should be considered during coadministration with CYP450 3A4 inducers. Alternative treatments may be required if an interaction is suspected.

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.