Simultaneous determination of aminopyrine and its metabolites in rat plasma by high-performance liquid chromatography

A simple and sensitive high-performance liquid chromatographic method has been developed for the quantitative determination of aminopyrine and eight of its metabolites (4-methylaminoantipyrine, 4-aminoantipyrine, 4-acetylaminoantipyrine, 4-acetylmethyl-aminoantipyrine, 4-hydroxyantipyrine, 4-formylaminoantipyrine, 3-hydroxymethyl-2-methyl-4-dimethylamino-1-phenyl-3-pyrazolin-5-one and 2-methyl-4-dimethylamino-5-oxo-1-phenyl-3-pyrazoline-3-carboxylic acid) in plasma of rats. The procedure includes a chloroform extraction prior to chromatography and quantitative analysis using peak-area ratios (ultraviolet absorbance detection at 260 nm) of aminopyrine and its metabolites to the internal standard, phenobarbital. The concentration—response curves for these compounds were linear from 20 ng/ml to 200 μg/ml. The extraction coefficients of aminopyrine and its metabolites from plasma were 80–100%. The coefficients of variation of intra- and inter-assay for these compounds in plasma were less than 2.5–5.5%. This method has been found to be applicable to the analysis of plasma samples obtained from aminopyrine-dosed rats.