Potential interaction w/ immunomodulating agents eg, cyclosporin; antihistamines eg, terfenadine, astemizole; macrolide antibiotics eg, erythromycin; azole antifungal eg, ketoconazole, itraconazole; rifampicin; medicines to regulate lipid levels eg, fibric acid derivatives, niacin, colestipol; some Ca channel blockers eg, nifedipine; some benzodiazepines eg, diazepam; PIs eg, nelfinavir; digoxin, warfarin, OCs, antacids, phenytoin. Avoid co-administration of strong CYP3A4 inhibitors (eg, ciclosporin, telithromycin, clarithromycin, delavirdine, stiripentol, ketoconazole, voriconazole, itraconazole, posaconazole & HIV PIs including ritonavir, lopinavir, atazanavir, indinavir, darunavir). Avoid concomitant use in patients taking telaprevir. Do not exceed 40 mg daily when taking w/ boceprevir. Do not drink >1-2 small glasses of grapefruit juice per day.