Osphos: The Latest Navicular Drug

A new remedy is doing wonders for sore-footed horses.
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A new remedy is doing wonders for sore-footed horses.

The horse

Soft Ride Boots

Rodeo horses are prime candidates to show signs of pain in their feet, considering the ground surfaces they’re often warmed up on and the thousands of miles they log on the hard floors of horse trailers. Team roping horses, in particular—both jackpot and rodeo—have a tendency to come up lame, not only due to soft-tissue injuries but often from chronic damage to bones in their feet.

The problem
When your rope horse comes up slightly lame, you know to have him checked for an injury to a tendon, ligament or muscle. It’s after that type of soft-tissue injury is ruled out that an x-ray might reveal a chronic condition like ringbone, joint arthritis or damage to the navicular bone (“navicular”).

When you’re roping a lot of steers, your horse’s skeletal structure responds to the stress by making new bone tissue. How it works is that “osteoclasts” eat away the old bone to make room for the new and denser bone, which is formed with the help of “osteoblasts.” 

In a horse that develops navicular or another chronic bone condition, the breakdown process happens faster than the rebuilding process. Until a handful of years ago, treatment options were limited to anti-inflammatory medications and corrective shoeing. Now there’s a drug that can actually inhibit bone degeneration—and thereby reduce pain.

The Solution

Osphos (pronounced “Oz-foz”) is made by Dechra Veterinary Products—the same folks who came out with IRAP serum. It was approved by the FDA in May and became commercially available in October. 

Like the French product Tildren, Osphos belongs to a class of drug that has been used to treat osteoporosis in humans. It has a different main ingredient than Tildren, though. In a field trial, 75 percent of lame horses improved, versus the Tildren trial in which 64 percent showed improvement.

Plus, Tildren has to be injected in the vein over an extended period while Osphos is injected in the muscle. A dose of Osphos costs between $300 and $500. When vets had to import Tildren from France, it cost $1,000 per dose, but the price should drop now that Tildren is also approved for sale in the U.S.

“If we can give these horses something that will help them internally, why not?” says Josh Harvey, DVM, who treats some of today’s top rope horses at Outlaw Equine in Decatur, Texas. “We’ve always had to try to treat every little injury as it comes, but with this drug we can actually hit several places at once—and even clean up bone edema that we may have missed.”

Edema refers to inflammation or swelling. Harvey says Osphos enters the bone tissue within 24 hours, and he’s seen clinical signs of navicular or bone pain improve seven days after injection. According to the field study, improvement is visible for at least two months after injection, with 65 percent of improved horses maintaining that improvement for six months.

“On an ultrasound, it can be very hard to see bone edema where the ligament attaches, but a horse can have immense pain in that location,” said Dr. Harvey. “With Osphos, we can reduce that pain. And since researchers are finding that subchondral bone tissue can affect cartilage, I’m not convinced this drug won’t also give us a chance to make joints healthier.”

Side effects of Osphos and Tildren aren’t considerably risky. Some horses get colicky just after injection, so watch for signs of stomach distress. And it’s advisable not to have the horse on Bute or any other anti-inflammatory at the time of injection, because the combination can be hard on kidneys. Also, neither drug should be given to broodmares or colts under 4 years old. The only other caveat is to make sure your veterinarian recognizes and addresses any related hoof issues. The ultimate objective should be helping the foot recover while reducing the pain.

“I really believe that a lot of these horses being hauled have bone edema, whether it’s in the pastern or the coffin or the canon bone,” said Dr. Harvey. “I’m excited that this treatment is so user-friendly and seems to last at least two months. Even for young horses in training whose feet are sore, if you rest them for two weeks and give them this, I’ve seen it help immensely.”