- Systemic treatment with corticosteroids or drugs known to be hepatic enzyme inducers or inhibitors within 14 days of study entry. Substances in these categories include macrolide antibiotics (e.g. erythromycin, clarithromycin), azole antifungals (e.g. ketoconazole, fluconazole, itraconazole), rifampin, rifabutin, and phenytoin.