Monitor Carefully (1)oxcarbazepine will reduce the level or effect of fentanyl by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Observe Carefully. Coadministration of fentanyl with CYP3A4 inducers could lead on to your lower in fentanyl plasma concentrations, deficiency of efficacy or, probably, development of the withdrawal