Watch Carefully (1)pentobarbital will lessen the level or result of fentanyl by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Keep an eye on Intently. Coadministration of fentanyl with CYP3A4 inducers could lead to your decrease in fentanyl plasma concentrations, lack of efficacy or, possibly, enhancement of the withdrawal s