pentobarbital will lessen the extent or impact of gefitinib by affecting hepatic/intestinal enzyme CYP3A4 metabolism.pentobarbital boosts effects of ifosfamide by impacting hepatic enzyme CYP2B6 metabolism. Use Caution/Watch. Coadministration of ifosfamide with CYP2B6 inducers may increase metabolism of ifosfamide to its metabolite. Watch for great