- Taking ketoconazole, voriconazole, itraconazole, erythromycin, telithromycin, clarithromycin, rifampin, rifabutin, bromocriptine, cimetidine, cisapride, clotrimazole, danazol, diltiazem, fluconazole, protease inhibitors (e.g., HIV and hepatitis C that include drugs such as ritonavir, indinavir, boceprevir, and telaprevir), metoclopramide, nicardipine, troleandomycin, verapamil, carbamazepine, phenobarbital, phenytoin, rifapentine, St. John's Wort (Hypericum perforatum), and grapefruit juice. Subjects on metformin will not be excluded.