Ketoconazole and rifampin significantly affect the pharmacokinetics, but not the safety or QTc interval, of casopitant, a neurokinin-1 receptor antagonist.

Casopitant, an antiemetic, is a neurokinin-1 receptor antagonist metabolized primarily by cytochrome P450 3A4 (CYP3A4). Three phase 1 studies with 131 healthy subjects examined the impact of a strong CYP3A inhibitor (ketoconazole) and inducer (rifampin) on the pharmacokinetics and safety of casopitant. Oral casopitant was administered alone (study 1, 100-mg single dose; study 2, 150 mg on day 1, 50 mg on days 2 and 3; study 3, 150-mg single dose) with either 400 mg daily of oral ketoconazole or 600 mg daily of oral rifampin.