Retrospective Detection and Deposition Profiles of Potentiated Sulphonamides in Equine Hair by Liquid Chromatography

Despite potential benefits of hair analysis to the equine industry, deposition of drugs in equine hair has been little studied. Trimethoprim/sulphonamides were selected as experimental ‘target’ drugs to investigate factors affecting drug uptake and distribution in equine hair. Hair samples were analysed by HPLC after extraction (0.2 M ammonium hydroxide, 60 °C, 24 h) and SPE (mixed-mode sorbent, C18/SCX). Analytes were resolved on a C18 column (150 × 2.1 mm, 4 μm) by gradient elution (25 mM triethylammonium phosphate, pH 3.0)/acetonitrile), detected at 240/270 nm, and identified by absorption spectra (225–360 nm). Calibration was linear from 0.125–25.0 ng.mg^?1. Recoveries were 71–93%. Sulphadimidine, sulphadiazine and trimethoprim were detected in hair from 12 horses. Hair colour and dose size affected the magnitude of drug uptake. Longitudinal distribution profiles of these drugs in tail hair were determined.