Check Carefully (one)phenobarbital will decrease the level or result of fentanyl transmucosal by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Intently. Coadministration of fentanyl with CYP3A4 inducers could lead on to the minimize in fentanyl plasma concentrations, not enough efficacy or, probably, advancement of