Simultaneous determination of dipyrone metabolites in rat hypothalamus, cerebrospinal fluid and plasma samples by LC-MS/MS

Background: After oral administration dipyrone is rapidly hydrolyzed to 4-methylaminoantipyrine, which is absorbed and further metabolized to 4-formylaminoantipyrine and to 4-aminoantipyrine, which is acetylated by a polymorphic N-acetyltransferase system to 4-acetylaminoantipyrine. To evaluate the presence of dipyrone metabolites in different rat matrices after intraperitoneal administration, an analytical method was developed and validated. Methodology: The four main dipyrone metabolites were extracted from plasma, cerebrospinal fluid and hypothalamus samples by LLE prior to LC-MS/MS. Results: Standard calibration graphs for all metabolites were linear (r > 0.99). The intra- and inter-day precision and accuracy values were both inferior to 15%. Conclusion: This method is simple and specific for studying dipyrone metabolites after intraperitoneal administration.