pentobarbital will decrease the extent or influence of tamoxifen by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Use Warning/Observe.pentobarbital will lower the level or impact of fentanyl transmucosal by affecting hepatic/intestinal enzyme CYP3A4 metabolism. Modify Therapy/Keep track of Intently. Coadministration of fentanyl with CYP3