Simultaneous determination of tramadol and its major active metabolite O-demethyltramadol by high-performance liquid...

A novel, highly sensitive method was developed for simultaneous determination of tramadol and its main active metabolite O-demethyltramadol (ODMT) in rat plasma. The method involves a single-step extraction procedure and a specific determination by high-performance liquid chromatography with electrochemical detection, using an ethoxy analogue of tramadol (L-233) as internal standard. The dual-electrode detector was operated in the oxidation-screening mode. Absolute recoveries of tramadol and ODMT were about 80%. Calibration curves were linear over a concentration range of 10-1000 ng/ml for ODMT and 10-10000 ng/ml for tramadol with intra- and inter-day coefficients of variation not exceeding 10% and 15%, respectively. The limit of quantification for tramadol and ODMT was lower than 15 ng/ml and 10 ng/ml using 100 microl of plasma, respectively. The described method allows an adequate characterization of the plasma vs. time profiles for both compounds.