Drug Interaction Report

GENERALLY AVOID: Coadministration with potent and some moderate inhibitors of CYP450 3A4 may significantly increase the plasma concentrations of simeprevir, which is primarily metabolized by the isoenzyme. In clinical trials, higher simeprevir exposures have been associated with increased frequency of adverse reactions including rash and photosensitivity. In 24 healthy study subjects administered simeprevir (150 mg once daily) in combination with the moderate CYP450 3A4 and P-glycoprotein substrate/inhibitor erythromycin (500 mg three times a day) for 7 days, mean simeprevir peak plasma concentration (Cmax), systemic exposure (AUC) and trough plasma concentration (Cmin) increased by approximately 4.5-, 7.5 and 12.7-fold, respectively. Erythromycin Cmax, AUC and Cmin also increased by about 1.6-, 1.9- and 3.1-fold, respectively, presumably due to inhibition of CYP450 3A4 and P-glycoprotein by simeprevir. In another study, simeprevir (200 mg once daily for 7 days) given with the potent CYP450 3A4 inhibitor ritonavir (100 mg twice daily for 15 days) to 12 healthy subjects resulted in approximately 4.7-, 7.2 and 14.4-fold increases in simeprevir Cmax, AUC and Cmin, respectively. Likewise, when simeprevir (50 mg and 150 mg once daily) was given with darunavir/ritonavir (800 mg/100 mg once daily) to 25 healthy subjects for 7 days, simeprevir Cmax, AUC and Cmin increased by about 1.8-, 2.6 and 4.6-fold, respectively, while ritonavir Cmax, AUC and Cmin increased by 1.2-, 1.3 and 1.4-fold, respectively. Darunavir Cmin increased by 1.3-fold.

MANAGEMENT: The use of simeprevir in combination with potent and some moderate CYP450 3A4 inhibitors such as azole antifungal agents, conivaptan, nefazodone, cobicistat, delavirdine, protease inhibitors, and ketolide and certain macrolide antibiotics should generally be avoided. Some authorities recommend avoiding concomitant use of simeprevir during and for 2 weeks after treatment with itraconazole.

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.

ADJUST DOSING INTERVAL: Food significantly enhances the oral bioavailability of simeprevir, although the type of food does not seem to matter. In healthy study subjects, administration of simeprevir after a high-fat, high-caloric (928 kcal) breakfast increased systemic exposure (AUC) by 61% and delayed absorption by 1 hour, while administration after a normal caloric (533 kcal) breakfast increased AUC by 69% and delayed absorption by 1.5 hours.

MANAGEMENT: To ensure maximal oral absorption, simeprevir should be administered with food.

The recommended maximum number of medicines in the 'protease inhibitors' category to be taken concurrently is usually one. Your list includes two medicines belonging to the 'protease inhibitors' category:

• fosamprenavir
• simeprevir

Note: In certain circumstances, the benefits of taking this combination of drugs may outweigh any risks. Always consult your healthcare provider before making changes to your medications or dosage.