ABSTRACT
A simple and sensitive column-switching HPLC method has been developed for the simultaneous determination of NK-104 (HMG-CoA reductase inhibitor) and its lactone in human and dog plasma. Plasma sample was extracted with methyl tert-butyl ether and then the extract was subjected to methylation with diazomethane to prevent the mutual conversion between NK-104 and its lactone. The extract was injected into the column-switching HPLC system. The calibration curves of NK-104 and NK-104 lactone were linear over the ranges 0.5 to 100 ng/ml for human plasma samples and 0.5 to 500 ng/ml for dog plasma, respectively. The intra-day and inter-day C.V. values of these analytes were less than 13.3%. The intra-day and inter-day accuracies of these analytes were between -14.0 and 6.5%. The proposed method has been applied to plasma samples obtained after oral administration of a single 2 mg dose of NK-104 to volunteers.
Subject(s)
Chromatography, High Pressure Liquid/methods , Hydroxymethylglutaryl-CoA Reductase Inhibitors/blood , Lactones/blood , Quinolines/blood , Animals , Dogs , Humans , Hydroxamic Acids/chemistry , Quinolines/chemistry , Rats , Reference Standards , Reproducibility of Results , Sensitivity and Specificity , Spectrophotometry, UltravioletABSTRACT
NK-104 is an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase with a very potent lipid-lowering effect. Biotransformation profiles of NK-104 in bile from rat, rabbit and dog given an intravenous infusion of NK-104 were investigated. Structural assignment was made by liquid chromatography (LC)-mass spectrometry (MS)-MS and proton NMR analyses. The predominant component was intact NK-104 in all the animals. At least eight other metabolites were present in rat, four in rabbit, and 10 in dog. These bile metabolites were purified and isolated by preparative HPLC. Biotransformation pathways elucidated for NK-104 were as follows: (a) lactonization ; (b) beta-oxidation of the side-chain; (c) hydroxylation of the quinoline ring; (d) conjugation with Beta-glucuronic acid and taurine. Beta-oxidative degradation of the side-chain in the case of other HMG-CoA reductase inhibitors is necessary for epimerization of the hydroxy group which has an R-configuration. However, M-16, glucuronide of the ketolactone derivative, was obtained as a key metabolite suggesting another beta-oxidation pathway for the side-chain.