Keep an eye on Carefully (1)oxcarbazepine will reduce the level or effect of fentanyl by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Check Carefully. Coadministration of fentanyl with CYP3A4 inducers may lead to some lower in fentanyl plasma concentrations, deficiency of efficacy or, maybe, advancement of the withdrawal sy