Monitor Intently (1)pentobarbital will lower the level or impact of fentanyl transdermal by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Observe Carefully. Coadministration of fentanyl with CYP3A4 inducers could lead to some lower in fentanyl plasma concentrations, deficiency of efficacy or, maybe, progress of a withdrawa