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Identification of p(4')-hydroxyantipyrine as a metabolite of antipyrine in man.

Several metabolites of antipyrine have been known for many years, but their recovery does not fully account for the drug in man. During the development of a HPLC assay of 3-hydroxymethylantipyrine, a major metabolite of antipyrine, the presence of another metabolite was noted. Its structure was postulated to be p(4')-hydroxyantipyrine (pOHA) on the basis of chemical derivatization and of mass spectrometry. The structure was confirmed by physicochemical comparison with a synthetic compound. The amount of pOHA in man is small, representing about 2-4% of the dose and less than 1% in the rat.