- Patients must not use the following known inducers of CYP3A4: carbamazepine, dexamethasone, ethosuxamide, glucocorticoids, griseofulvin, nafcillin, nelfinavir nevirapine, oxcarbazepine, phenobarbital, phenylbutazone, phenytoin, primidone, progesterone, rifabutin, rifampin, rofecoxib, St John's Wort, sulfadimidine, sulfinpyrazone, troglitazone, efavirenz, modafinil, and rifapentine; drugs that induce CYP3A4 enzymes can cause reductions in ZD1839 plasma concentrations below levels thought to be biologically active