Metabolism Of Ketamine In The Cytochrome P450 Of Human Liver Microsomes

To provide the profiles of metabolism of ketamine by human liver microsomes ketamine was incubated with human liver microsomes, and NADPH as cofactor, detected by HPLC. The metabolism of ketamine in human liver microsomes was studied to identify the effects of CYP450 inhibitors and enzyme kinetics of the metabollism of ketamine.A HPLC method was developed to determine ketamine and its metabolites. Chromatography was performed on a Hypersil ODS2 column (20cm×4.6mm, 5μm)with acetonirile-0.025mol/Lphosphate buffer-triethylamine(46: 54: 0.02, v/v/v) as mobile phase. The detection wavelength was 21 lnm.The enzyme kinetics of ketamine N-demethylation was biphasic.this indicates that at least two enzyme systems are responsible for the N-demethylation pathway of ketamine.the Vmax was5.44pmol/min/pmol P450, Km value was45.7umol/L, and the intrinsic clearance(Vmax/ Km)was 119×10^-6ml/min/ pmol P450 for the high affinity/low capacity enzyme. For the low affinity/high capacity enzyme, Vmax, Km, Vmax/ Km were 12.01pmol/min/ pmol P450, 1875.3μmol/L and 6.4×10^-6ml/min/ pmol P450, respectively. The in vitro total intrinsic clearance of ketamine in human liver microsomes was 26.2×10^-6 ml/min/ pmol P450. N-demethylation of ketamine into norketamine accounts for more than 80% of the total microsomal oxidation process of ketamine in human liver microsome.The results suggest that CYP2B6 is suppose to be the main enzyme of ketamine metabolism in human liver microsome. Two-tailed t-test shows significant individual difference (p value＜0.05).