Detection of Cyclosporine in Horse Hair After Ocular Implant Administration

ABSTRACT

This study describes the detection and temporal distribution of cyclosporine in equine hair following ocular implant administration in a Thoroughbred gelding. Mane hair samples were collected at 172‐ and 217‐day post‐implantation and analysed by liquid chromatography–tandem mass spectrometry (LC‐MS/MS) after alkaline hydrolysis and liquid–liquid extraction. The method achieved an estimated limit of detection of 0.1 pg/mg. Cyclosporine was detected in hair at both sampling time points, with segmental analysis revealing distribution patterns consistent with systemic exposure and incorporation during hair growth. Peak concentrations were observed in distal segments corresponding to the period of implantation, whereas proximal segments in the later sample were below the detection limit, indicating declining exposure over time. To our knowledge, this study provides the first evidence of an exogenous peptide drug being incorporated into equine hair. The prolonged detectability of cyclosporine in hair highlights its potential as a complementary matrix for long‐term monitoring of peptide drug exposure in equine sports.