"No one's put the oral [product] in a rigorous, scientific model of osteoarthritis and shown that it works," says McIlwraith. "But I can't say that it doesn't work. There's just no data yet."
Obtaining the data to prove the efficacy of a new drug in horses is no small task. Earning FDA approval "costs millions of dollars and years of bureaucracy," says Scott Pierce, DVM, a veterinarian with Kinetic Technologies, LLC, who developed the oral HA preparation called Conquer.
Companies can have many reasons for electing to bring a product like this to market without full FDA approval as a drug. In this case, says Pierce, it was decided that the ultimate sales of the oral preparation most likely would not be extensive enough to cover the costs of the research that would be required for approval.
But Pierce says he has conducted a few small studies that have yielded promising results. In one, 26 Thoroughbreds in race training were given daily oral doses of either a placebo gel or a gel containing 100 milligrams of sodium hyaluronate for 59 days. During that time, the horses' trainers were asked to note the number of days the horses were worked, the number of days they were just walked, and whether they were referred to veterinarians for lameness exams or radiographs.
On average, the horses in the treated group were galloped on the track for five extra days
compared to the horses given the placebo. "Also, 11 of the 13 horses in the placebo group were referred for a lameness exam, and only four in the treated group were examined for lameness," Pierce says. "The numbers may be small, but that's statistically significant."
In another study with 10 horses divided into three groups, Pierce showed that oral administration can increase the levels of HA in the blood. In other words, it appears to be absorbed through the horse's intestinal walls, but no one has proven that HA has any therapeutic value when administered that way.
When HA is Right for Horses
HA can be invaluable for treating the earliest stages of joint inflammation. Numerous studies conducted since the 1970s have shown that HA injections are most effective when they are used to treat mild to moderate cases of synovitis--inflammation of the synovial membrane--and capsulitis, inflammation of the joint capsule. Both can be caused by either a single trauma or by repeated stress, and the signs include lameness and painful swelling in the affected joint.
But HA is not a cure-all for every joint ill. The injections do little to help a joint with a tearing injury, which can produce signs similar to those caused by inflammation alone, nor is HA effective against advancing osteoarthritis.
"If significant chipping or degradation of the joint has already occurred, HA is not a very good treatment," McIlwraith says. That's one reason why FDA regulations require that both forms of HA injection be administered only by veterinarians--an accurate diagnosis is necessary to be sure that the drug is being used effectively.
The easy availability of oral HA means that horsekeepers now have the option of administering it on their own, and many people choose to use it prophylactically in horses who work hard enough to be at risk for joint troubles but who have never shown signs of lameness, as well as in older horses with generalized stiffness but no specific signs of arthritis. While the effectiveness of oral supplements may be uncertain, horse owners can be assured that they will do no harm.
"As far as we know, it has no side effects," says McIlwraith. Nevertheless, he emphasizes that if a horse is showing any signs of lameness, it is important for him to see a veterinarian for a thorough examination before a preparation of any kind is administered.
This article originally appeared in the June 2004 issue of EQUUS magazine.
