Elimination profiles of flurbiprofen and its metabolites in equine urine for doping analysis.

Flurbiprofen and its main acidic metabolites were detected in equine urine after a single-dose administration of 500 mg flurbiprofen to two 2.5-3.5-years-old mares, in order to be used in equine doping control routine analysis. The urine levels of the parent drug were determined using GC/MS. Five acidic metabolites were found in the urine. The structure of the proposed metabolites was confirmed by HRMS accurate mass measurements. The highest flurbiprofen concentration was 204 mug ml(-1) at 1-3 h post administration. Flurbiprofen could be detected for 24-37 h in urine using the standard screening procedure. All metabolites were present 25 h post administration, while 4'-hydroxyflurbiprofen could be traced for more than 48 h and it is regarded as the long-term metabolite of flurbiprofen in horse.