THE FATE OF AMINOPYRINE (PYRAMIDON) IN MAN AND METHODS FOR THE ESTIMATION OF AMINOPYRINE AND ITS METABOLITES IN BIOLOGICAL MATERIAL

Abstract

Methods are described for the estimation of Pyramidon and two of its metabolites, 4-aminoantipyrine and N-acetyl 4-aminoantipyrine, in biological fluids and tissues. Factors concerned with the physiological disposition and metabolic fate of Pyramidon in man have been studied. The drug is absorbed almost completely from the gastrointestinal tract and is then fairly evenly distributed throughout the body water. Only about 3 per cent of the drug is excreted in the urine, the rest being transformed in the body. The rate of transformation varies from 10 to 30 per cent an hour in different individuals. A major step in the metabolism of Pyramidon in man involves demethylation to form 4-aminoantipyrine, an active analgesic and antipyretic. This compound is acetylated in large part to N-acetyl 4-aminoantipyrine, which seems to be pharmacologically inert. A minor fraction of Pyramidon is converted to 4-hydroxyantipyrine which is excreted in a conjugated form. About 50 per cent of the Pyramidon is unaccounted for. The analgesic and antipyretic activity of Pyramidon is exerted only in part through 4-aminoantipyrine; it is probable that the parent compound is also an active analgesic.