In 2014 the FDA approved bisphosphonates to control signs of navicular disease in horses age 4 and up, changing the way veterinarians manage performance horses of all disciplines. To evaluate their use in the five years since, Dechra, maker of the intramuscular injectable bisphosphonate Osphos, recently organized a roundtable of English and Western sport horse practitioners.
Rob Boswell, DVM, an English sport horse veterinarian based in Wellington, Florida, and Billy Maupin, DVM, who treats Western performance horses in Nampa, Idaho, summarized the discussion’s take-homes during a Dechra-sponsored Sunrise Session at the 2019 American Association of Equine Practitioners Convention, held Dec. 7-11 in Denver.
Bisphosphonates primarily work by preventing excess bone resorption, which occurs with navicular disease (aka podotrochlosis) and other bone disorders. They might offer the additional benefit of reducing bone pain. While bisphosphonates are labeled for navicular treatment alone, Boswell and Maupin said veterinarians use them off-label in other lameness cases.
“It’s been a game-changer as a standalone and adjunct therapy,” said Boswell. “In some cases, it has made a difference in horses when I don’t know what’s going on, but I think it’s bone-related. It’s dramatically increased the weapons with which I can attack many common problems.”
Diagnostic imaging, horse age, and type of work the horse is doing dictate whether veterinarians administer bisphosphonates.
“Accurate diagnosis is paramount,” said Boswell.
Regarding diagnostic imaging findings, “I’m looking for radiographic or scintigraphy (bone scan) changes,” said Maupin. “If they light up on a bone scan (e.g., in the pelvis or sacroiliac joint area), I’m pretty much going to reach for Osphos—same with radiographic changes in the feet.”
Hot spots on bone scans indicate abnormal bone metabolism, and “anything that could be associated with abnormally increased bone metabolism is a candidate for Osphos,” said Boswell.
Boswell said he expects definite short-term improvements in navicular-related within seven to 10 days of administering bisphosphonates. In his practice, he redoses horses two weeks later, then again two weeks after that, for a total of three full doses over 30 days. Horses can stay in normal work throughout this period. Going forward, he doesn’t administer Osphos again unless he needs to.
“This isn’t a drug you circle on a calendar,” said Maupin. “If your horse is sound, you don’t need to give the drug again. If he’s still sore, do more diagnostics.”
“They’re consistently doing better,” said Boswell. “I don’t see horses becoming lame soon. It’s also dramatically decreased the frequency with which I need to perform joint injections.”
Texas-based practitioner and roundtable attendee Chris Ray, DVM, said it’s not unusual in his practice for horses with navicular pain to improve at least two lameness grades after bisphosphonate therapy.
Navicular horses should look better after 14 days and still be good after four months, said FEI veterinarian Marc Koene, DVM.
The veterinarians agreed that bisphosphonates are almost always part of a multimodal approach to treating an issue. Concurrent therapies and considerations might include joint injections, Adequan or Legend, and hoof support and shoeing.
Known potential side effects of bisphosphonates include gastrointestinal signs and renal (kidney) toxicity, particularly if administered in conjunction with NSAIDs.
“I’ll ask the client when the horse’s last dose of NSAIDs was,” said Boswell. “I like to have a two-day window before and after giving Osphos in which the horse doesn’t receive NSAIDs.”
He said he also makes sure the horse is well-hydrated. Occasionally a horse shows colic signs or strange behavior, which he said typically go away within 10 minutes.
While safe to administer at once, Maupin said his approach to avoiding any renal effects is to split the bisphosphonate dose over three days.
Both veterinarians feel comfortable administering Osphos off-label for conditions besides navicular pain.
“It’s been the best drug in a long time to get horses back in the show pen and reduce the use of non-steroidal anti-inflammatories (NSAIDs) and injections for any lytic (involving bone loss) disease,” said Maupin.
Editor’s Note: Using bisphosphonates to treat any other condition besides navicular pain is considered an off-label use.