pentobarbital boosts toxicity of ifosfamide by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Use Warning/Keep an eye on. CYP3A4 inducers might enhance the metabolism of ifosfamide to its Energetic alkylating metabolites.pentobarbital will reduce the extent or outcome of theophylline by affecting hepatic/intestinal enzyme CYP3A4 metabolism.