Abstract: In order to investigate the pharmacokinetics of the enantiomers of O-demethyltramadol, the active metabolite of trans tramadol, twelve healthy male volunteers were given multiple oral doses of trans tramadol hydrochloride sustained-release tablets. The enantiomers of O-demethyltramadol in serum were analyzed with high-performance capillary electrophoresis (HPCE). For (+)- and (-)-O-demethyltramadol, Tmax were 3.75±1.25 h and 3.38±1.00 h, Cmax were 18.20±7.31 ng·mL^-1 and 22.80±5.55 ng×mL^-1, and AUC0~t were 162.09±64.96 ng·mL^-1×h and 178.89±46.72 ng×mL^-1×h, respectively. In each subject, the average ratio of (-)/(+)-O-demethyltramadol in the serum at all sampling time points was between 0.89 and 1.90. But at each sampling time point, the average ratio in different subjects was similar. It could be concluded that the stereoselectivity in pharmacokinetics of O-demethyltramadol was different among human subjects.

Key words: Trans tramadol, Trans tramadol, O-Demethyltramadol, O-Demethyltramadol, Enantiomer, Enantiomer, Pharmacokinetics, Pharmacokinetics, Stereoselectivity, Stereoselectivity