Monitor Closely (one)phenobarbital will lower the extent or impact of fentanyl transmucosal by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Monitor Intently. Coadministration of fentanyl with CYP3A4 inducers could lead into a lessen in fentanyl plasma concentrations, lack of efficacy or, possibly, advancement of the withd