Keep an eye on Carefully (one)pentobarbital will decrease the extent or effect of fentanyl by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Observe Intently. Coadministration of fentanyl with CYP3A4 inducers may lead to a minimize in fentanyl plasma concentrations, deficiency of efficacy or, perhaps, growth of the withdrawal