Check Closely (one)phenobarbital will decrease the level or influence of fentanyl transmucosal by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Observe Closely. Coadministration of fentanyl with CYP3A4 inducers could lead into a lessen in fentanyl plasma concentrations, insufficient efficacy or, quite possibly, enhancement o