Quantitative gas-liquid chromatographic method for the determination of indomethacin in biological fluids

A sensitive and specific gas chromatographic method for the analysis of indomethacin has been developed. After extraction of the drug from blood or urine with ethylene dichrloride a derivative is formed with pentafluorobenzyl bromide. 5-Fluoro-indomethacin is used as an internal standard. The overall recovery of indomethacin is 85.1 +/- 2.3% and the method can detect 10 ng indomethacin in a 1 ml plasma or urine sample. No interference in the method is seen with some commonly used drugs. The method has been used to measure plasma indomethacin concentrations in 20 patients with rheumatoid arthritis, being treated with 25 mg indomethacin three times daily. The plasma concentration ranged from 168-596 ng/ml.