pentobarbital will reduce the level or influence of etoposide by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Use Caution/Watch.pentobarbital will lower the level or result of tramadol by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Use Warning/Observe. Diminished AUC of tramadol and the active metabolite (O-desmethyltramado