HPLC DETERMINATION OF XYLAZINE IN EQUINE PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A high performance liquid chromatographic (HPLC) method is described for the determination of xylazine in equine plasma. The drug and internal standard (pindolol) were separated on a 5 mum cyanopropyl-modified column (250 x 4.6 mm i.d.) using a buffer-acetonitrile mixture containing an ion pairing reagent. The drug and internal standard were isolated from plasma by liquid extraction into ethyl acetate. The method was validated over the concentration range 50-2000 ng/ml in plasma; the reproducibility, expressed as the mean co-efficient of variation was less than 5.0% for both between-day and within-day replicate determinations. The method was linear over the concentration range studied. No interferences were observed from endogenous plasma components and the limit of detection was 20 ng/ml. The method was successfully applied to the determination of xylazine in equine plasma in a crossover study design for pharmacokinetic measurements.