Watch Closely (one)oxcarbazepine will reduce the level or effect of fentanyl by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Check Intently. Coadministration of fentanyl with CYP3A4 inducers could lead to your minimize in fentanyl plasma concentrations, deficiency of efficacy or, possibly, growth of the withdrawal syndrome