ORTHOPEDICS

Bone Drug Can Linger in Horse Blood, Urine

By Adam Marcus Traces of a tightly regulated drug to treat bone loss in horses can appear in blood and urine for 1,000 days or longer after even a single injection of the medication, researchers in Hong Kong have found.

Tiludronic acid belongs to a class of agents called bisphosphonates, which physicians and veterinarians use to prevent fractures in people, and to treat navicular lameness in horses. Racing bodies have strict rules about the administration of tiludronic acid in horses; the medication—which inhibits the skeleton from

Racing bodies have strict rules about the administration of tiludronic acid in horses.

breaking down existing bone—is banned in animals younger than 3.5 years of age, in whom it can significantly retard skeletal growth; and within 30 days of a race, as it can act as an analgesic that might mask a painful injury to bone that racing might worsen.

However, most conventional testing does not detect tiludronic acid in either the urine or blood of animals. Although bisphosphonates are difficult to detect, some labs are able to use special methods to screen for bisphosphonates, but such tests may not be performed regularly, making the drugs vulnerable to abuse by unscrupulous veterinarians, trainers and breeders.

As the researchers note, “Conditions of sales of most bloodstock auction companies globally now have specific statements relating to detection of bisphosphonates in horses sold through them, with the condition that the sale may be rendered void by the purchaser if bisphosphonates are detected in blood samples collected within a specified period following the ‘fall of the hammer’.”

The new study suggests those periods might be too short: Tiludronic acid can linger in the body for years — you just have to know how to look for it.

Led by Chris Riggs, PhD, DEO, DECVS, MRCVS, director of the Equine Welfare Research Foundation, and chief advisor of Veterinary Science at the

Hong Kong Jockey Club, the researchers used a technique called ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) to search for traces of tiludronic acid in 24 horses that had received injections of the drug for various approved clinical conditions. At the club, veterinarians can administer tiludronic acid only if they first receive permission from the head of the center.

“The necessary use of all equine medications and all clinical procedures are strictly controlled and monitored at the Hong Kong Jockey Club, which has provided us with excellent treatment records and traceability of our horses to conduct this survey,” Dr. Riggs told Modern Equine Vet. “Given that a proportion of a dose of bisphosphonate drug administered to an animal binds to mineral in bones throughout the body and effectively becomes ‘locked’ into the skeleton, it was reasonable to hypothesize that we might detect a low concentration of the drug in blood and urine a very long time after a dose was administered as it is slowly released during the slow but steady process of background bone metabolism. We wished to test this hypothesis.”

The UHPLC-HRMS tests revealed traces of tiludronic acid in all 24 of the samples, 2 of which had been taken from horses that had received single injections of the drug 3 years earlier. Concentrations of the medication typically were lower in urine than in blood, but not always, according to the researchers. MeV Shutterstock/dikkenss

For more information:

Riggs C, et al. Tiludronic acid can be detected in blood and urine samples from Thoroughbred racehorses over three years after last administration. Equine Vet J. 2020 Nov 28 [Epub ahead of print]. https://pubmed.ncbi.nlm.nih.gov/33247964/