Quantitative analysis of the dihydropyridines, 3-(2-furoyl)-5-methoxycarbonyl-2,6-dimethyl-4-(2-nitrophenyl)- 1,4-dihydropyridine and nifedipine, by high-performance liquid chromatography with electrochemical detection.

An analytical method based on solvent extraction and reversed-phase high-performance liquid chromatographic separation with electrochemical detection has been developed for the dihydropyridines, 3-(2-furoyl)-5-methoxycarbonyl-2,6-dimethyl-4-(2-nitrophenyl) -1,4-dihydropyridine (MDL 72.567) and nifedipine. The analysis includes an internal standard of similar light sensitivity to correct for possible photodegradation during the procedure. The specificity of electrochemical detection precludes interference from oxidized metabolites. Total analysis time was 35 min per sample, and the detection limit for quantification was 1-2 ng/ml. Linear regression analysis gave calibration curves with coefficients or correlation of 0.9992 for MDL 72.567 (1-100 ng) and 0.997 for nifedipine (1-50 ng). Assays for within-run and day-to-day reproducibility gave coefficients of variation of 3.9% and 6.0%, respectively, at concentrations of 50 ng/ml. The method has been applied to the analysis of plasma levels of nifedipine and MDL 72.567 in dogs.