Treating Joint Pain in HorsesBy Kentucky Equine Research Staff · March 2, 2017
Direct administration of anti-inflammatory corticosteroid drugs into joints to provide relief from discomfort remains a common practice in many sectors of the equine industry. Those medications, including betamethasone, triamcinolone, and methylprednisolone, decrease inflammation, but evidence exists they can potentially damage articular cartilage, rather than protect it, masking injuries that would otherwise prevent a horse from performing and placing that horse in danger of further injury.
Corticosteroid use continues to be tightly regulated in various sports, including Thoroughbred racing. According to Knych and colleagues*, the current guideline for betamethasone is 10 pg/mL measured in a blood sample seven days after administration of a single 9-mg dose into one or more joints of a horse.
While widely adopted as the official “withdrawal time,” Knych argues that only one study was performed to generate this data. He further notes that measuring drug levels of a particular drug in a blood or urine sample does not necessarily reflect the drug levels at the site of administration.
“Both triamcinolone acetonide and methylprednisolone acetate are detected in the joint for prolonged periods of time relative to their detection time in blood or urine,” wrote Knych and coworkers.
In fact, the researchers indicated that triamcinolone was measurable in synovial fluid for 35 days after a single intra-articular administration but could not be measured in blood a mere seven days after administration. This means that the drug persists in the joint and could potentially be effective for much longer than originally suspected, warranting less frequent administration.
To test this theory with betamethasone, researchers administered 9 mg of betamethasone in the middle carpal joint, or knee, of 12 Thoroughbred racehorses. Supporting the accepted withdrawal time for betamethasone, the drug was no longer detectable by 96 hours post-administration; however, it could still be detected at the site of administration for up to 21 days in some horses.
According to the researchers, these results suggest that “blood concentrations should not be used as an indicator of the duration of pharmacologic effect.”
"Corticosteroids such as betamethasone frequently provide relief for horses suffering joint pain, but studies show that preventing joint disease prior to trauma or any sort of wear and tear is also an effective approach to managing joint health. Joint supplements containing glucosamine, chondroitin sulfate, avocado-soybean unsaponifiables, hyaluronic acid, omega-3 fatty acids all support equine joint health,” reminded Kathleen Crandell, Ph.D., a nutritionist for Kentucky Equine Research (KER).
*Knych, H.K., S.D. Stanley, L.M. Harrison, et al. Pharmacokinetics of betamethasone in plasma, urine and synovial fluid following intra-articular administration to exercised Thoroughbred horses. Drug Testing and Analysis. In press.