Watch Closely (1)phenobarbital will lower the extent or outcome of fentanyl transmucosal by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Observe Intently. Coadministration of fentanyl with CYP3A4 inducers may lead to some minimize in fentanyl plasma concentrations, insufficient efficacy or, possibly, advancement of a with