Western Australia has witnessed a growing incidence of therapeutic substances, originally intended for human use, being detected and reported in race-day samples. Recently, these detections have encompassed second and third generation antipsychotic drugs. The potential use of antipsychotic drugs in racehorses poses a serious challenge to the integrity of equine sports and animal welfare. These compounds, developed for human psychiatric treatment, are not registered for veterinary use in performance horses in Australia and are classified as prohibited substances under most racing regulations. Antipsychotic drugs, also categorized as neuroleptics or major tranquilizers, are known to reduce agitation and induce calming effects, raising concerns about their potential misuse to alter equine behaviour or performance.
Clozapine and aripiprazole, two atypical antipsychotics, were detected during routine screening of race-day plasma samples. Their respective metabolites, desmethylclozapine and dehydroaripiprazole were also tentatively identified. Unlike other human drugs reported in race-day equine samples that are excreted largely unchanged, clozapine and aripiprazole undergo extensive metabolism in humans. This results in only trace amounts of the unchanged parent compounds being present in human urine. Therefore, the commonly proposed explanation of inadvertent environmental exposure by means of unhygienic practices such as urination in stables is unlikely to account for the presence of these compounds in equine samples.
This study details the detection of clozapine and aripiprazole in race-day plasma samples in Western Australia using a targeted liquid chromatography-high resolution accurate mass-mass spectrometry method. The study also examines the plausibility of environmental exposure as a potential source. To the authors knowledge, these drugs have not previously been reported in equine plasma in Australia. This investigation highlights the need to continually broaden the scope of routine screening methods, particularly to include human therapeutic substances such as newer-generation antipsychotics, to uphold fairness in the racing industry and safeguard animal welfare.