Observe Closely (1)phenobarbital will minimize the level or outcome of fentanyl transmucosal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Keep an eye on Carefully. Coadministration of fentanyl with CYP3A4 inducers could lead on to some decrease in fentanyl plasma concentrations, not enough efficacy or, probably, progress