pentobarbital increases toxicity of ifosfamide by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Use Warning/Check. CYP3A4 inducers may boost the metabolism of ifosfamide to its active alkylating metabolites.pentobarbital will decrease the extent or outcome of clozapine by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/M