pentobarbital will lessen the extent or influence of tramadol by influencing hepatic/intestinal enzyme CYP3A4 metabolism. Use Warning/Monitor. Decreased AUC of tramadol and also the active metabolite (O-desmethyltramadol) when coadministered with robust CYP3A4 and CYP2B6 inducerspentobarbital decreases results of hemin by pharmacodynamic antagonism