A disposition kinetic study of tramadol in rat perfused liver.

A recirculated perfusion system was used to investigate the metabolism of tramadol, an analgesic agent, in the isolated perfused rat liver. Tramadol was added to the perfusion medium at a concentration of 300 ng/ml, and the perfusate samples were collected for 180 min. The concentration of tramadol and its three main metabolites O-desmethyltramadol (M1) and N-desmethyltramadol (M2) and N,O-didesmethyltramadol (M5) were determined in perfusate samples by a rapid HPLC method.