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

A high performance liquid chromatographic (HPLC) method is described f or the determination of xylazine in equine plasma. The drug and intern al standard (pindolol) were separated on a 5 mum cyanopropyl-modified column (250 x 4.6 mm i.d.) using a buffer-acetonitrile mixture contain ing an ion pairing reagent. The drug and internal standard were isolat ed from plasma by liquid extraction into ethyl acetate. The method was validated over the concentration range 50-2000 ng/ml in plasma; the r eproducibility, expressed as the mean co-efficient of variation was le ss than 5.0% for both between-day and within-day replicate determinati ons. The method was linear over the concentration range studied. No in terferences were observed from endogenous plasma components and the li mit of detection was 20 ng/ml. The method was successfully applied to the determination of xylazine in equine plasma in a crossover study de sign for pharmacokinetic measurements.