Hair analysis as a novel investigative tool for the detection of historical drug use/misuse in the horse: a pilot study.

REASONS FOR PERFORMING STUDY: Analysis of human hair for drug residues is being used increasingly as a diagnostic tool in the investigation of drug use and abuse. Hair analysis is complementary to urine/blood testing in that it can provide an extensive historical record of drug use, is noninvasive, impersonal and can facilitate retesting. However, the technique has not been studied in horses. HYPOTHESIS: That the systemic administration of drugs in horses could be identified by the detection of drug residues in hair. OBJECTIVE: To evaluate hair analysis as a potential retrospective diagnostic test for drug administration in horses by studying the deposition of systemically administered drugs in tail hair. METHODS: Tail hairs (n = 40-50) from 4 horses with known drug histories were washed, chopped into 3-5 mm fragments and extracted overnight, in 0.1 mol/l hydrochloric acid, prior to solid-phase extraction and analysis by high-performance liquid chromatography. Horse 1, a 3-year-old Thoroughbred colt (gastric ulcer), was treated for 14 days with omeprazole; Horse 2, a 3-year-old Thoroughbred colt (anaerobic infection), was treated for 5 days with metronidazole; Horse 3, an 8-year-old Thoroughbred gelding (sinusitis), was treated for 10 days with trimethoprim/sulphadiazine; and Horse 4, a 3-year-old Thoroughbred colt (respiratory infection), was treated for 5 days with procaine benzylpenicillin. RESULTS: Omeprazole was not detected in tail hair. Metronidazole was detected in tail hair at a concentration of 0.57 ng/mg, trimethoprim and sulphadiazine at concentrations of 9.14 and 2.26 ng/mg, respectively, and procaine at a concentration of 1.66 ng/mg. CONCLUSIONS: The data presented suggest that hair analysis may become a useable technique for the retrospective detection of drug administration in horses. POTENTIAL RELEVANCE: This technique could ultimately be used as part of a prepurchase veterinary examination to identify misuse of anti-inflammatory and sedative drugs, in an in-training testing programme to identify use of anabolic agents, or to provide evidence to support post race blood or urine test results. Clearly, more extensive research will be required to evaluate the effectiveness of the technique over a much broader range of drugs.