Determination of xylazine and its metabolites by GC-MS in equine urine for doping analysis

Xylazine and its main metabolites were detected in equine urine after a single-dose intravenous administration of 0.98 and 1.01 mg/kg body weight xylazine, respectively, in two horses, in order to be used for equine doping control routine analysis. The urine levels of the parent drug and its metabolites were determined using gas chromatography-mass spectrometry (GC-MS). Xylazine is metabolised rapidly, down to a concentration level of about 1.0 mug/ml after 1-3 h administration. Seven metabolites were identified in urine. 4-Hydroxy-xylazine, the major metabolite, could be traced for 25 It and it is regarded as the long-term metabolite of xylazine in horse. 2,6-Dimethylaniline was, for the first time, reported as metabolite in equine. (C) 2003 Elsevier B.V. All rights reserved.