Abstract
In order to investigate the pharmacokinetics of quinidine in the horse, an extractionfluorescence method was developed for determination of quinidine in equine plasma. Plasma quinidine concentrations were determined by two fluorescence methods, which were the protein precipitate (PP) method and the extraction (EX) method. Although there was an excellent correlation of results between the two methods (r=0.943, P<0.001), the value determined by the PP method was twice as large as that by the EX method. It was presumed that the higher concentration by the PP method might have been obtained by such contamination with quinidine metabolites as noticed in human plasma. In order to elucidate the true concentration of quinidine and to exclude its metabolites, the same plasma samples were assayed comparatively by very specific high-performance liquid chromatography (HPLC) and the EX method. There was an excellent correlation (r=0.975, P<0.001) in results and a good consistency in value between the two methods. From these findings, it was concluded that the EX method was more accurate and specific than the PP method and might be available for a study of pharmacokinetics of quinidine in the horse.
