If your horse isn’t performing well due to joint inflammation and pain, a veterinarian may suggest injecting an anti-inflammatory corticosteroid into the affected joint. Four products currently have approval by the U.S. Food and Drug Administration for intra-articular use, including isoflupredone acetate (IPA). Surprisingly, little data has been collected on the impact of IPA within the joint or its duration of action.

“Based on research involving two other intra-articular medications, methylprednisolone and triamcinolone, equine experts* suggest that IPA may actually exert beneficial effects long after it can be detected in the blood,” explained Laura Petroski, B.V.M.S., veterinarian for Kentucky Equine Research (KER).

To test this theory, Knych and colleagues from the School of Veterinary Medicine at the University of California, Davis, devised a system to measure the effect and duration of effect of intra-articular corticosteroid drugs. Specifically, the system measured the expression of various pro-inflammatory mediators and degradative enzymes that can harm the joint.

“Previous studies on triamcinolone showed that this particular intra-articular corticosteroid had a long duration of action, exerting beneficial effects long after the medication could be detected in a horse’s bloodstream,” relayed Petroski.

In the current study, 12 healthy horses undergoing a stringent exercise regime received either 8 mg of IPA into the radiocarpal joint (the topmost joint of the knee) or just saline. Blood and synovial fluid samples were subsequently collected at specific time points up to 42 days following administration. Key findings included:

  • In treated horses, IPA levels in blood and synovial fluid were below the “level of detection” between 14 and 21 days following intra-articular administration;
  • Compared to the expression of various genes at baseline, immediately prior to IPA administration, altered expression—both increased and decreased—was noted for thousands of genes in synovial fluid; and
  • Of those, a significant increase in the expression of the Annexin A1 gene was noted up to 42 days after IPA administration. This gene produces a potent anti-inflammatory protein that blocks key steps in the arachadonic acid cascade and was not increased in the control horses;
  • In addition, significant decreases in the levels of the inflammatory mediator interleukin 23A as well as enzymes that degrade articular cartilage (matrix metalloproteinases 1 and 9) were noted for up to 42 days following treatment.
  • The researchers concluded that the results of this study advance understanding of the anti-inflammatory nature of intra-articular administration of IPA and that IPA appears to have a prolonged effect relative to detection time in the bloodstream and joint fluid.Either in lieu of or in addition to intra-articular corticosteroids, the use of certain oral joint health products can also help maximize the health of equine joints. Consider using high-quality products such as KER•Flex and Synovate HA to help maintain the health and integrity of the joint tissues, including the articular cartilage lining the ends of bones within joints.“In Australia, horse owners should look to Glucos-A-Flex, a blend of glucosamine hydrochloride, vitamins, minerals, and amino acids, for joint support,” recommended Petroski.

    Each of the four FDA-approved corticosteroid drugs has clear guidelines regarding the amount to be injected into a joint, the total amount used in the horse, and the number of hours or days the medication must be administered prior to competition to avoid a positive drug test result.

    *Knych, H.K., L. Harrison, N. Chouicha, et al. Expression of inflammatory and structural matrix genes in synovial fluid following intra-articular administration of isoflupredone acetate to exercised horses. Equine Veterinary Journal. In press.