- No cytochrome P450, family 3, subfamily A, polypeptide 4 (CYP3A4) inducers within 7 days prior to starting protocol therapy and while on protocol treatment; CYP3A4 inducers include phenytoin, carbamazepine, barbiturates, rifampin, St John's Wort, dexamethasone, modafinil, and rifapentine; single doses of dexamethasone used as an antiemetic are permitted