Keep track of Carefully (1)pentobarbital will lower the extent or influence of fentanyl transdermal by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Watch Intently. Coadministration of fentanyl with CYP3A4 inducers could lead on to a decrease in fentanyl plasma concentrations, lack of efficacy or, possibly, enhancement of th