Initial results of a study conducted at the University of Kentucky Gluck Equine Research Center suggest accepted dosage levels for several corticosteroids commonly used in racing may be worth further study.
At the Kentucky Equine Drug Research Council meeting March 12 in Lexington, Dr. Jamie MacLeod outlined initial results of a study that looked at the efficacy and dangers of methylprednisolone, betamethasone, and triamcinolone, which are used to treat ailing joints in racehorses.
The study concluded that the desired therapeutic effects of the corticosteroid treatments, especially methylprednisolone and betamethasone, could be accomplished at lower dosage levels than recommended by the manufacturer and commonly used on the backstretch. MacLeod said as dosage levels increase, more negative side effects were observed.
MacLeod said more study is needed to determine the proper dosage levels to use corticosteroids to treat inflammation and pain but avoid negative side effects that include death of healthy cells in the joint.
The study initially noted the various levels at which corticosteroids killed healthy cells outside the horse. Then the study saw the same effects within the horse, when horses were injected in the fetlock with corticosteroids. The alternate fetlock, used as a control, was injected with a placebo.
MacLeod again saw negative side effects, like death of healthy cells, in the fetlocks treated with the corticosteroids. MacLeod said at lower doses, the therapeutic side effects occurred with little or no adverse side effects.
MacLeod believes recommended dosage levels may be too high to begin with and he noted that, in practice, some horses may be receiving significantly more than the recommended level. He said he knows that to be the case in Quarter Horse racing.
"We need a dose large enough for efficacy but small enough to avoid cell death," MacLeod said of the recommended dosage, which he said currently appears to be closer to the level that causes cell death than the level needed for efficacy. "I am not opposed to corticosteroids; they can be highly beneficial. I think we can find a better dose to achieve those goals."
KEDRC member and veterinarian Andy Roberts noted that many racetrack veterinarians already give doses lower than the recommended maximum level.
MacLeod said veterinarians who routinely administer corticosteroids, or high levels of corticosteroids, will not see added benefits. He said because 100% efficacy is reached at a relatively low dosage level. Any levels above that, only add the negative side effects without adding any therapeutic benefit.