Watch Carefully (1)phenobarbital will lessen the extent or outcome of fentanyl transmucosal by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Observe Carefully. Coadministration of fentanyl with CYP3A4 inducers could lead on to your lessen in fentanyl plasma concentrations, not enough efficacy or, perhaps, improvement of a