Biohydroxylation of aminopyrine: quantitative studies of 3-hydroxymethyl metabolite in rats

Significance of the formation of 4-dimethylamino-3-hydroxymethyl-2-methyl-1-phenyl-3-pyrazolin-5-on e (AM-3-CH2OH) for the metabolism of AM was examined quantitatively in rats. Although urinary excretion of AM-3-CH2OH accounted for only 0.7% to the dose, incubation of AM in the isolated hepatocyte system resulted in the formation of 9% of AM-3-CH2OH. Furthermore, metabolic disappearance of AM-3-CH2OH in the same system was fast, indicating the properties of an intermediate metabolite. These results suggested that the metabolic pathways via AM-3-CH2OH are very important in the metabolism of AM.