Observe Closely (1)phenobarbital will decrease the level or influence of fentanyl transmucosal by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Carefully. Coadministration of fentanyl with CYP3A4 inducers could lead to a lower in fentanyl plasma concentrations, deficiency of efficacy or, maybe, enhancement of the wit