Drug Interaction Report

Based on in vitro data, coadministration with potent inhibitors of CYP450 3A4 and/or 2C19 may be expected to increase the plasma concentrations of ambrisentan, which is a substrate of these isoenzymes. However, administration with ketoconazole (potent CYP450 3A4 inhibitor) or omeprazole (potent CYP450 2C19 inhibitor) did not result in clinically relevant changes in ambrisentan exposure.

ADJUST DOSING INTERVAL: Food may reduce the systemic bioavailability of amprenavir from fosamprenavir oral suspension. The mechanism of interaction has not been described. According to the product labeling, administration of fosamprenavir oral suspension (1400 mg single dose) with a high-fat meal (967 kcal, 67 g fat, 33 g protein, 58 g carbohydrate) reduced amprenavir peak plasma concentration (Cmax) by 46% and systemic exposure (AUC) by 28% compared to administration in a fasted state. The time to reach peak plasma level (Tmax) was delayed by 0.72 hours. In contrast, the same high-fat meal did not affect the pharmacokinetics of amprenavir from fosamprenavir tablets.

MANAGEMENT: Fosamprenavir suspension should be administered on an empty stomach in adults, but with food in pediatric patients to aid palatability and compliance. If emesis occurs within 30 minutes after dosing the suspension, the dose should be repeated. Fosamprenavir tablets may be taken with or without food.