pentobarbital boosts toxicity of ifosfamide by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Watch. CYP3A4 inducers may increase the metabolism of ifosfamide to its active alkylating metabolites.pentobarbital will lower the extent or outcome of tolterodine by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Wa