- Caution should be exercised when dosing ketoconazole, rifampin, omeprazole, midazolam, tolbutamide, and dextromethorphan concurrently with CYP3A4 substrates, inducers, and/or inhibitors; furthermore, patients who are taking concurrent medications that are strong inducers/inhibitors or substrates of CYP3A4 should be switched to alternative medications to minimize any potential risk; if such patients cannot be switched to alternative medications, they will be ineligible to participate in this study