Simultaneous determination of morniflumate and its major active metabolite, niflumic acid, in human plasma by high-performance liquid chromatography in stability and pharmacokinetic studies.

A rapid, sensitive and stable high-performance liquid chromatography (HPLC) method was developed and validated for the simultaneous determination of morniflumate and its major active metabolite, niflumic acid, in human plasma. HPLC analysis was carried out using a 5 µm particle size, C18 -bonded silica column with a mixture of acetonitrile and 0.005 m potassium phosphate monobasic in water (60:40, v/v) as the mobile phase and UV detection at 287 nm. The method involved the treatment with 50 μL of 0.4 m hydrochloric acid for the stability of morniflumate, extraction with diethylether and evaporation to dryness under a nitrogen stream. The lower limit of quantitation for morniflumate and niflumic acid was 50 and 500 ng/mL, respectively. The calibration curves for morniflumate and niflumic acid were linear over the concentration range of 50-20,000 ng/mL and 500-50,000 ng/mL, respectively, with correlation coefficients greater than 0.9995 and inter- or intra-batch coefficients of variation not exceeding 13.79%. The variability (percentage difference) of incurred sample re-analysis did not exceed 11.72% and all of the repeat samples fell within 20% of the mean value. This assay procedure was applied successfully to an examination of the pharmacokinetics of morniflumate and its metabolite, niflumic acid, in human subjects.