Title: Determination of mefenamic acid in horse plasma by high performance liquid chromatography.
Abstract: A high performance liquid chromatographic procedure was developed for the quantitative analysis of mefenamic acid in horse plasma. To a 0.25 ml plasma sample, 25 μg of internal standard was added, and was extracted with methylene chloride under acidic conditions. Portions of the organic layer were evaporated to dryness under nitrogen gas. 'The residues were reconstituted in methanol and injected onto a column packed with Cosmosil 5C18. The elution was performed with a mixed solvent of methanol and 2% acetic acid (70 : 30, v/v) at 40°C. The flow rate was 2 ml/min, and the effluent was monitored at 352 nm. Mefenamic acid and the internal standard eluted at 8.8 and 11.2 min, respectively. The peak area ratio (mefenamic acid/internal standard) versus plasma concentration was linear in the range of 0.150μg/ml of mefenamic acid in plasma, and the detection limit of mefenamic acid was 0.05μg/ml. This method was successfully applied to the determination of mefenamic acid in the horse plasma after drug administration.