Keep an eye on Intently (1)pentobarbital will decrease the extent or result of fentanyl by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Watch Closely. Coadministration of fentanyl with CYP3A4 inducers may lead to some lessen in fentanyl plasma concentrations, not enough efficacy or, quite possibly, growth of the withdrawa