Check Closely (1)phenobarbital will minimize the extent or impact of fentanyl transmucosal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Observe Closely. Coadministration of fentanyl with CYP3A4 inducers could lead into a lower in fentanyl plasma concentrations, insufficient efficacy or, quite possibly, improvement of a w