pentobarbital will decrease the extent or effect of tamoxifen by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Keep an eye on.pentobarbital will lower the extent or impact of tramadol by impacting hepatic/intestinal enzyme CYP3A4 metabolism. Use Warning/Keep an eye on. Diminished AUC of tramadol and the Energetic metabolite (O-