Simultaneous stereoselective analysis by capillary electrophoresis of tramadol enantiomers and their main phase I metabolites in urine

Capillary zone electrophoresis was successfully applied to the enantiomeric resolution of racemic tramadol and its six phase I metabolites using carbo xymethylated beta-cyclodextrin (CMB) added to the background electrolyte (B GE). Baseline resolution of tramadol and its metabolites was obtained in le ss than 30 min using a 50 mM phosphate buffer (pH 2.5) containing 5 mM of C MB. Chiral determinations of tramadol and its main three metabolites, O-dem ethyltramadol (M1), N-demethyltramadol (M2) and O-demethyl-N-demethyltramad ol (M5), were performed in urine after a simple double liquid-liquid extrac tion of 200 mu l of biological material. In the tested concentration range (0.5-20 mu g/ml. except for MZ: 0.5-10 mu g/ml) coefficients of correlation superior than 0.994 were obtained. Within-day variation determined on thre e different concentrations for each enantiomers showed accuracies ranging f rom 95.4% to 103.2%. The relative standard deviation (RSD) of these assays was determined to be less than 10.0%. Day-to-day variation presented accura cies ranging from 96.3% to 106.5% with a RSD less than 9.0%. After oral adm inistration of 100 mg of tramadol hydrochloride to an healthy volunteer, th e urinary excretion was monitored during 30 h. About 15% of the dose was ex creted as unchanged tramadol. The enantiomeric ratios of all the excreted a nalytes, T, M1, M2 and M5, were found to be very different to 1.0, showing that a stereoselective metabolism of tramadol clearly occurred. (C) 1999 El sevier Science B.V. All rights reserved.