Check Intently (one)phenobarbital will decrease the extent or impact of fentanyl transmucosal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Intently. Coadministration of fentanyl with CYP3A4 inducers may lead into a lessen in fentanyl plasma concentrations, deficiency of efficacy or, perhaps, development of a with