Determination of tenoxicam, and the isolation, identification and determination of Ro 17-6661, its major metabolite, in human urine.

A high-performance liquid chromatographic method for the determination of tenoxicam (Ro 12-0068, I) and the hydroxy metabolite Ro 17-6661 (II) in human urine has been developed. The parent drug and metabolite were extracted from acidified urine by means of an Extrelut column with chloroform. The evaporated eluate was analysed on a C18 reversed-phase column with methanol-phosphate buffer as the mobile phase and UV detection at 371 nm. The detection limit for both compounds in a 1-ml sample was 50 ng/ml (C.V. 7%). The inter- and intra-assay precision up to 20 micrograms/ml was 3-6%. The method was applied to the analysis of I and II in the urine of a human subject who had received a 40-mg oral dose of the drug. Approximately 36% of the dose was eliminated in the urine as II, and less than 0.5% as unchanged I. After enzymatic hydrolysis of the urine, an extra 2% of the dose was found as II. Compound II was isolated from human urine by preparative thin-layer chromatography and identified by comparison of its mass and proton resonance spectra with those of an authentic specimen.