Abstract: AIM: To establish a new method for parameter estimation in enzyme kinetics by AUC, and then to analyze the metabolism of two enantiomers of metoprolo (Met) in rat liver by the method. METHODS: The formula was derived by mathematical method.In the slices incubation technique the concentration was determined for two enantiomers of Met on three different dose (5, 10, and 30 μmol·L ^-1), their enzyme kinetic parameters was estimated by the method obtained in this paper. RESULTS: The values of AUC differed significantly (P < 0.01) for two enantiomers of Met on three different doses, The values of v_m and k_m were 5.7471 and 6.7724 μmol·L ^-1 for R-(+) -Met, respectively, and 6.430 and 18.3404 μmol·L ^-1 for S-(-)-Met. CONCLUSION: Enzyme kinetic model is suitable for the study on liver metabolism of drug.Elimination pharmacokinetics is differed significantly for two enantiomers of Met in rat liver slices, and the metabolism was stereoselective.

Key words: pharmacology, enzyme kinetics, metoprolo, enantiomer, parameter estimation