Keep track of Carefully (1)pentobarbital will reduce the level or impact of fentanyl transdermal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Intently. Coadministration of fentanyl with CYP3A4 inducers could lead on to the lessen in fentanyl plasma concentrations, deficiency of efficacy or, perhaps, enhancement o