DETERMINATION OF INDOMETHACIN AND MEFENAMIC-ACID IN PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Indomethacin and mefenamic acid are widely used clinically as non-ster oidal anti-inflammatory agents. Both drugs have also been found effect ive to produce closure of patent ductus arteriosus in premature neonat es. A simple, rapid, sensitive and reliable HPLC method is described f or the determination of indomethacin and mefenamic acid in human plasm a. As these drugs are not applied together, the compounds are alternat ely used as analyte and internal standard. Plasma was deproteinized wi th acetonitrile, the supernatant fraction was evaporated to dryness an d the resulting residue was reconstituted in the mobile phase and inje cted into the HPLC system. The chromatographic separation was performe d on a C-18 column (250 x 4.6 mm I.D.) using 10 mM phosphoric acid-ace tonitrile (40:60, v/v) as the mobile phase and both drugs were detecte d at 280 nm. The calibration graphs were linear with a correlation coe fficient (r) of 0.999 or better from 0.1 to 10 mu g/ml and the detecti on limits were 0.06 mu g/ml for indomethacin and 0.08 mu g/ml for mefe namic acid, for 50-mu l plasma samples. The method was not interfered with by other plasma components and has been found particularly useful for paediatric use. The within-day precision and accuracy of the meth od were evaluated for three concentrations in spiked plasma samples. T he coefficients of variation were less than 5% and the accuracy was ne arly 100% for both drugs.