The latest in bisphosphonates for horses – The Horse

The latest in bisphosphonates for horses – The Horse

Two bisphosphonates approved by the FDA for use in horses older than 4 years are available on the US market: tiludronate disodium (Tildren) and clodronate disodium (Osphos). It’s essential to note that they are not approved for use on racehorses, says Allen. He acknowledges that other bisphosphonate products are available, some of which are potent and promising, but drugs other than the two mentioned here are prohibited from use in almost all competitive disciplines.

Here’s what researchers know about the use of bisphosphonates and future opportunities for further research.

Findings of recent studies

To date, the largest study looking at the use of bisphosphonates in horses is the 2022 article “Retrospective Analysis of Tiludronate Use in Equine Practice: Safety in 1,804 Horses, Efficacy in 343 Horses,” published in the Equine Veterinary Science Journal.

Allen and Richard D. Mitchell, DVM, MRCVS, Dipl. ACVSMR, of Fairfield Equine Associates, in Newtown, Connecticut, provided data for the study. His records included notes on the evolution of each horse’s degree of lameness, side effects observed, and subsequent return to performance. All horses received a slow intravenous (IV) administration of tiludronate 1 mg/kg between 2006 and 2019.

The results:

  • 82% of the horses competed at a similar or better level after treatment.
  • More than 80% of the horses initially scored 1.5/5 on the lameness scale and were healthy 30 days after treatment.
  • Side effects were experienced by 0.9% of the horses.

In a recent review of clodronate (Markell et al., 2020), the authors concluded that equine studies have consistently shown the drug to have a good therapeutic effect and a good safety profile when used to treat scaphoid bone disease . “But we need larger studies to better understand how useful it is in various cases,” says Allen.

At UC Davis, Knych, Associate Professor Carrie Finno, DVM, PhD, and a team of researchers are conducting studies to expand the body of knowledge about clodronate. Their study, “Clodronate detection and effects on markers of bone resorption are prolonged after a single administration to horses,” was published in the journal Equine Veterinary Journal in July.

The study, funded by the Grayson Jockey Club and the Viola Foundation, included 11 horses, a limitation Knych acknowledged. Seven exercised thoroughbreds received 1.8 mg/kg clodronate and four received the same dose of saline. Knych says his goal was to better understand how bisphosphonates affect the long-term health and fitness of equine athletes.

“It was also intended to provide information that would help regulate bisphosphonates in horse racing,” he adds.

The researchers found that clodronate was detectable in blood for 14 to 175 days and in urine for up to 175 days. In some horses, Knych says, drug concentrations were undetectable at one time point but detectable at a later time point.

“It wasn’t necessarily a surprise but rather interesting to see that the drug can stay in the body for so long after a single administration,” he says, noting that in a 2021 study, his team found that a horse retained a bisphosphonate in bone. for 18 months.

“Similar to what we see in humans (the half-life of bisphosphonates in human bone is several years), the drug resides in the horse’s body for a long period of time, which can prolong the drug’s effect.” “, she says. “In humans, clinicians often recommend a ‘drug holiday’ after prolonged use due to the long residence time and potential for drug accumulation. This prolonged effect has been associated with a higher incidence of fractures and healing problems.”

Administration varies by drug. As noted, veterinarians administer tiludronate intravenously.

Allen says monitoring the horse after treatment is critical. For example, excessive drinking or urination could indicate an underlying kidney problem that had not been previously observed. For this reason, some veterinarians perform blood tests to assess kidney function prior to administration. Although side effects are low (0.9%), they could include a mild colic-like episode.

“We would support the horse with more fluids in this case,” he says. “However, in my experience and in our study, this is extraordinarily rare.”

In contrast, clodronate is given by intramuscular injection and also carries minimal risks, but the side effects are slightly different. For example, the horse may experience pain at the injection site. Researchers from human studies have described the use of lidocaine with an injection to reduce pain, but this is rare in equine medicine, says Allen.

“Most commonly in veterinary medicine, we sedate the horse before administration and then let the horse wake up and watch the horse for 30 minutes after the injection to make sure it’s okay,” he says.

Clodronate can also aggravate underlying kidney problems, so watch for a horse to drink or urinate excessively for two to three days after treatment.

“These are reasonable things on both drugs,” adds Allen.

Veterinarians also advise against the simultaneous administration of bisphosphonates and nonsteroidal anti-inflammatory drugs, such as flunixin meglumine, in horses due to potential kidney damage.

Learned lessons

While bisphosphonates were first introduced into equine medicine to treat navicular pain, their use may be a game changer in other situations. For example, Allen says that studies indicate that tiludronate has significantly reduced the development of osteoarthritis in horses.

“Say you put a cast on a horse,” he says. “You know that (the injured limb) will lose bone density because it is not being used. It occurs in humans and horses. A study that treated a horse with Tildren found that it was effective in reducing the amount of osteoarthritis and associated accepted pain.”

Bisphosphonates are valuable tools in equine practice, he says, especially for horses that may once have been sidelined from their careers or lived in discomfort. However, as their use has expanded and additional studies have been published, veterinarians have learned several key lessons about these drugs.

First, they shouldn’t be used on horses younger than 4 years old, says Allen. Young horses have active growth plates. Because bisphosphonates are designed to inhibit bone absorption, the use of these drugs in young horses interferes with the development of bone structures. It is also not advisable to give bisphosphonates to pregnant mares. As with all mammals, changes to bone and cartilage occur in the womb, and those natural processes should not be disturbed, says Allen.

Leave a Comment