- Inability to discontinue a prescription or non-prescription drugs or other products known to be metabolized by CYP3A4, or to inhibit or induce CYP3A4 prior to Day 1 of dosing and to withhold throughout the study until 2 weeks after the last dose of study medication. Medications of particular concern are the following inhibitors of CYP3A4: azole antifungals (ketoconazole itraconazole, fluconazole and voriconazole), macrolide antibiotics (erythromycin, clarithromycin), cimetidine, aprepitant, HIV protease inhibitors, nefazodone and the following inducers of CYP3A4: phenytoin, barbiturates and rifampicin. Substrates of CYP3A4 include statins (lovastatin, simvastatin), midazolam, terfenadine, astemizole, and cisapride.