Keep track of Carefully (1)pentobarbital will lower the extent or influence of fentanyl by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Check Closely. Coadministration of fentanyl with CYP3A4 inducers could lead on to a decrease in fentanyl plasma concentrations, deficiency of efficacy or, perhaps, enhancement of the with