- Prescribed or over the counter (OTC) drugs that are potent cytochrome P450 (CYP) 3A4 inhibitors (e.g., ketoconazole), CYP3A4 substrates with higher affinity (e.g., verapamil, diltiazem), or potent CYP3A4 inducers (e.g., rifampicin, phenytoin, carbamazepine), including natural and herbal remedies (e.g., St. John's Wort) within 14 days prior to intake of study drug at Day 1