phenobarbital improves toxicity of ifosfamide by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Use Warning/Observe. CYP3A4 inducers may possibly enhance the metabolism of ifosfamide to its active alkylating metabolites.Watch Closely (one)phenobarbital will minimize the extent or outcome of tofacitinib by impacting hepatic/intestinal enzyme