pentobarbital will lower the extent or influence of fosamprenavir by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Keep an eye on.pentobarbital improves effects of ifosfamide by affecting hepatic enzyme CYP2B6 metabolism. Use Warning/Monitor. Coadministration of ifosfamide with CYP2B6 inducers may raise metabolism of ifosfamide