Drug Interaction Report

ADJUST DOSE: Coadministration with moderate inducers of CYP450 2C9 or 3A4 may decrease the plasma concentrations and therapeutic effects of erdafitinib. The mechanism is induction of CYP450 2C9- or 3A4-mediated metabolism of erdafitinib, which has been shown to be metabolized by these isoenzymes.

MANAGEMENT: According to the manufacturer, if a moderate CYP450 2C9 or 3A4 inducer is coadministered at the start of erdafitinib therapy, the recommended dose of erdafitinib should be administered. If a moderate CYP450 2C9 or 3A4 inducer is coadministered after the initial dose increase period, the dose of erdafitinib may be increased up to 9 mg once daily based on serum phosphate levels and tolerability. When a moderate CYP450 2C9 or 3A4 inducer is discontinued, the current dose of erdafitinib may be continued in the absence of erdafitinib toxicity.

ADJUST DOSING INTERVAL: Food enhances the oral bioavailabilities of both elvitegravir and tenofovir. When a single dose of cobicistat/elvitegravir/emtricitabine/tenofovir (trade name Stribild) was given with a light meal (approximately 373 kcal; 20% fat), mean elvitegravir and tenofovir systemic exposures (AUCs) increased by 34% and 24%, respectively, relative to fasting conditions. When administered with a high-fat meal (approximately 800 kcal; 50% fat), the mean AUC of elvitegravir and tenofovir increased by 87% and 23%, respectively, relative to fasting conditions. The alterations in mean AUCs of cobicistat and emtricitabine were not clinically significant with either the light or high-fat meal.

MANAGEMENT: Cobicistat/elvitegravir/emtricitabine/tenofovir as a fixed-dose preparation should be administered once daily with food. Elvitegravir as a single-ingredient preparation should also be administered once daily with food.