High-performance liquid chromatography of dipyrone and its active metabolite in biological fluids.

New high-performance liquid chromatography methods were developed to measure dipyrone and its active metabolite 4-monomethylaminoantipyrine (MAA) in biological fluids. While no detectable level of the unchanged dipyrone was found in plasma of four subjects taking 1000-mg oral doses of the drug, values ranging from 1.25 to 14.99 micrograms/ml of MAA were observed. Twenty-four hour urinary excretion of MAA varied from 9.56 to 21.21 mg. Concentrations as low as 0.25 micrograms/ml of MAA can be measured with acceptable coefficients of variation. The method, therefore, is suitable for microquantification of MAA in biological fluid which enables convenient and rapid assessment of the drug disposition in body.