Quantitation of 6-(pyridin-3-yl)quinolin-2(1H)-one, a cardiac stimulant, and its N-oxide metabolite in dog plasma by high-performance liquid chromatography.

A method is described for the determination of UK-57,400 (I), a 6-substituted quinoline cardiotonic, and its pyridyl-N-oxide in dog plasma. The analytes are selectively retained from plasma (1 ml) on a solid-phase extraction column and eluted with 1 ml of methanol. After evaporation to dryness, the residue is reconstituted in 100 microliters of the mobile phase. Chromatography is carried out on a Spherisorb 5 microns phenyl high-performance liquid chromatography column, with ultraviolet detection. Calibration curves are linear for concentrations from 10 to 100 ng ml-1. For I, the coefficients of variation at highest and lowest concentrations are 1 and 14%, respectively, while the corresponding figures for the pyridyl-N-oxide metabolite are 4 and 10%, respectively. Sample recovery from extraction is greater than 90%. The limit of detection is 4 ng ml-1 for both analytes.