A rapid and sensitive high performance liquid chromatography-mass spectrometry （HPLC-MS） method for the quantification of nimesulide in human plasma was developed and validated. Sample aliquots of 100μL were extracted by one-step liquid-liquid extraction after addition of hydrochlorothiazide as the internal standard （IS）. Analytes were separated on a reverse phase C18 column using methanol-water （84：16, v/v） as the mobile phase and detected by a single quadrupole mass spectrometer in selected ion monitoring （SIM） negative mode. Monitored m/z values for nimesulide and IS were 307.00 and 295.90, respectively. The overall run time was 4.2 min. Validation experiments demonstrated good precision and accuracy over a wide concentration range of 20.0-7000 ng/mL with a lower limit of quantification （LLOQ） at 20.0 ng/mL. No interference by endogenous substances or matrix effect was observed. Average extraction recoveries for nimesulide and IS were all greater than 84.4%. The assay was successfully applied to a bioequivalence study of nimesulide dispersible tablets in Chinese male volunteers after oral administration.
