Monitor Intently (one)phenobarbital will lessen the level or impact of fentanyl transmucosal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Keep track of Carefully. Coadministration of fentanyl with CYP3A4 inducers may lead into a lower in fentanyl plasma concentrations, insufficient efficacy or, quite possibly, advancemen