Observe Closely (one)phenobarbital will minimize the extent or outcome of fentanyl transmucosal by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Watch Carefully. Coadministration of fentanyl with CYP3A4 inducers could lead to some decrease in fentanyl plasma concentrations, lack of efficacy or, maybe, growth of the withdrawa