Tiludronic acid can be detected in blood and urine samples from Thoroughbred racehorses over three years after last administration

BACKGROUND Administration of bisphosphonates, including tiludronic acid, to Thoroughbred racehorses below three and a half years of age is prohibited in most racing jurisdictions. OBJECTIVES To determine if evidence of administration of tiludronic acid could be obtained from analysis of blood and urine samples beyond 40 days after administration. STUDY DESIGN Retrospective cohort. METHODS Horses maintained in a highly controlled environment and treated with Tildren®a were selected from clinical records. Twenty four horses were identified, 21 of which were still in race training. Blood and urine samples were collected and analysed for the presence of tiludronic acid using ultra-high performance liquid chromatography-high resolution mass spectrometry. RESULTS Tiludronic acid was detected in samples from every horse, including two that had been given a therapeutic dose of the drug three years prior to sample collection. The estimated concentrations of tiludronic acid in the blood collected at least two years post administration were consistently very low (less than 0.3 ng/mL). The estimated concentrations in urine were less consistent and were generally lower than in blood although higher levels were inconsistently detected in individual horses (up to about 16 ng/mL almost one year post administration in one horse and about 3.7 ng/mL at almost three years post administration in another). MAIN LIMITATIONS The study was performed in horses that are older than the primary target group. A single sample was obtained from most horses and so we cannot comment on elimination profiles. CONCLUSIONS Evidence that a therapeutic dose of tiludronic acid has been administered to a horse can be obtained from detection of the drug in blood and urine samples over three years after it was administered.