Check Intently (one)pentobarbital will reduce the level or result of fentanyl by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Keep track of Carefully. Coadministration of fentanyl with CYP3A4 inducers may lead into a decrease in fentanyl plasma concentrations, lack of efficacy or, quite possibly, advancement of a withdrawal