Increased plasma conc of CYP3A4 substrates eg, pimozide, terfenadine, astemizole, cisapride, dexamethasone, methylprednisolone, midazolam, alprazolam, triazolam. Decreased plasma conc of CYP2C9 substrates eg, S(-) warfarin, tolbutamide, phenytoin. Caution & careful monitoring when co-administered w/ chemotherapeutic agents metabolized primarily or in part by CYP3A4 eg, etoposide, vinorelbine, docetaxel, ifosfamide, cyclophosphamide, irinotecan, paclitaxel. Post-marketing events of neurotoxicity after co-administration w/ ifosfamide. Efficacy of hormonal contraceptives may be reduced during & for 28 days after administration of Emend. Increased plasma conc w/ strong CYP3A4 inhibitors eg, ketoconazole. Decreased plasma conc w/ strong CYP3A4 inducers eg, rifampin. Increased AUC of aprepitant & diltiazem. Decreased AUC of aprepitant & paroxetine.