Quantitation of nimesulide in human plasma by high-performance liquid chromatography with ultraviolet absorbance detection and its application to a bioequivalence study.

A rapid and simple high-performance liquid chromatography-reversed phase (HPLC-RV) method with ultraviolet detection (258 nm) was developed and validated for the quantitation of nimesulide (CAS 51803-78-2) in human plasma. After the plasma samples were extracted with 6.0 ml of dichloromethane containing the internal standard phenacetin 2 microg/ml in methanol, the analysis of the nimesulide level in the plasma samples was carried out using a reverse phase Supelcosil LC-18 (15 cm x 4.6 mm x 5 pm) column. The chromatographic separation was accomplished with an isocratic mobile phase consisting of a mixture of methanolphosphate buffer (pH 3.5; 0.01 mol/l) (55:45, v/v). The inter-assay accuracy ranged from 103.4 to 113.2%, while intra-day ranged from 105.6 to 117.5%. The inter-assay precision ranged from 11.7 to 14.6%, while intra-assay ranged from 3.2 to 9.5%. The recovery of nimesulide was determined as part of the assay validation process and was excellent. The linearity of the nimesulide curves ranged from 0.20 to 15.0 microg/ml (y = 0.3857-0.0081, r = 0.9975). Short-term stability showed that nimesulide is stable in plasma for at least 24 h at room temperature, while long-term stability studies showed that nimesulide is stable in plasma for at least 180 days when stored at -20 degrees C. This validated method was successfully applied to the bioequivalence study of nimesulide in tablets in healthy volunteers.