- Selected strong inhibitors of cytochrome P450, family 3, subfamily A, polypeptide 4 (cytochrome P450 3A4) include azole antifungals, such as fluconazole, voriconazole, itraconazole, ketoconazole, and strong inducers include drugs such as rifampin, phenytoin, phenobarbitol, carbamazepine, and St. John's wort; the use of these drugs should be avoided with vincristine (vincristine sulfate)