Check Carefully (1)phenobarbital will lower the extent or outcome of fentanyl transmucosal by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Watch Intently. Coadministration of fentanyl with CYP3A4 inducers could lead on to some minimize in fentanyl plasma concentrations, lack of efficacy or, probably, advancement of the wi