Watch Carefully (one)phenobarbital will decrease the level or result of fentanyl transmucosal by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Keep an eye on Closely. Coadministration of fentanyl with CYP3A4 inducers could lead on into a lessen in fentanyl plasma concentrations, not enough efficacy or, quite possibly, progre