SIMULTANEOUS MEASUREMENT OF PROGUANIL AND ITS METABOLITES IN HUMAN PLASMA AND URINE BY REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY, AND ITS PRELIMINARY APPLICATION IN RELATION TO GENETICALLY-DETERMINED S-MEPHENYTOIN 4'-HYDROXYLATION STATUS

A simple high-performance liquid chromatographic (HPLC) assay method w as developed for the measurement of proguanil (PG) and its major metab olites, cycloguanil (CG) and 4-chlorophenylbiguanide (CPB), in human p lasma and urine. The assay allowed the simultaneous determination of a ll analytes in 1 ml of plasma or 0.1 mi of urine. The detection limits of PG, CG, and CPB, defined as the signal-to-noise ratio of 3, were 1 and 5 ng/ml for plasma and urine samples, respectively. Recoveries of the analytes and the internal standard (pyrimethamine) were > 62% fro m plasma and > 77% from urine. Intra-assay and interassay coefficients of variation for all analytes in plasma and urine were < 10% except f or the values of CG and CPB, which ranged from 10% to 15% at one or tw o concentrations among 4-5 concentrations studied. The clinical applic ability of the method was assessed by the preliminary pharmacokinetic study of PG, CG, and CPB in six healthy volunteers with the individual ly known phenotypes (extensive and poor metabolizers) of S-mephenytoin 4'-hydroxylation, suggesting that individuals with a poor metabolizer phenotype of S-mephenytoin have a much lower capacity to bioactivate PG to CG compared with the extensive metabolizers.