Watch Carefully (one)pentobarbital will decrease the level or impact of fentanyl transmucosal by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Keep an eye on Intently. Coadministration of fentanyl with CYP3A4 inducers could lead on to the decrease in fentanyl plasma concentrations, lack of efficacy or, perhaps, growth of the