pentobarbital boosts toxicity of ifosfamide by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Use Warning/Keep an eye on. CYP3A4 inducers could increase the metabolism of ifosfamide to its active alkylating metabolites.pentobarbital will decrease the extent or outcome of etonogestrel by impacting hepatic/intestinal enzyme CYP3A4 metabolism.