Observe Intently (one)phenobarbital will lessen the extent or influence of fentanyl transmucosal by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Watch Carefully. Coadministration of fentanyl with CYP3A4 inducers could lead into a lower in fentanyl plasma concentrations, insufficient efficacy or, maybe, improvement of a with