Observe Intently (one)oxcarbazepine will decrease the level or effect of fentanyl by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Keep track of Closely. Coadministration of fentanyl with CYP3A4 inducers may lead to a lower in fentanyl plasma concentrations, insufficient efficacy or, quite possibly, improvement of the withdr