Simultaneous determination of the main metabolites of dipyrone by high-pressure liquid chromatography

A simple, rapid, and sensitive procedure is described for the determination of the main metabolites of dipyrone in plasma and urine. After adding isopropyl aminoantipyrine as internal standard and a deproteinizer the plasma of urine samples are alkalized and extracted with chloroform. The residue of the evaporated organic phase is dissolved in mobile phase and separated by HPLC. The compounds are detected by ultraviolet light at 265 nm. The following metabolites can be determined selectively by this method: 4-methylamino-antipyrine, 4-aminoantipyrine, 4-formylaminoantipyrine and 4-acetylaminoantipyrine. The detection limit for all four metabolites is 0.1 microgram/ml in plasma and 2 micrograms/ml in urine. The results of a human pharmacokinetic study are also presented.