Detection Times of Clodronic Acid in Horses with Orthopedic Disease.

Clodronic acid is designated as a controlled medication for competition horses by the International Federation for Equestrian Sports and, according to the International Federation of Horseracing Authorities, clodronic acid is not to be administered to racehorses younger than 3.5 years or within 30 days prior to a race. In this study, 35 horses involved in competition were treated with a single dose of 1.53 mg clodronic acid/kg bodyweight intramuscularly. Plasma samples were obtained before treatment and 10, 20, 30, and 40 days post-administration. Clodronic acid concentrations were measured using a validated method, and the data were fitted using a nonlinear mixed effects model. The estimated depletion half-life of clodronic acid was 10.6 days (inter-individual variability: 17.9%). Age, body weight, sex, disease severity, dose, training days, training, and competition did not significantly impact the depletion half-life. The percentage of horses predicted via simulation to have clodronic acid concentrations below the assay's limit of quantification of 1.0 ng/mL was 93.9% at day 30 and 99.4% at Day 40. This study provides rationale to the equestrian federations and horse racing authorities to reliably establish a detection time for clodronic acid, assisting equine veterinarians in recommending a competition withdrawal time for the horses under their care.