Residual effects of intra-articular betamethasone and triamcinolone acetonide in an equine acute synovitis model.

BACKGROUND Intra-articular (IA) corticosteroids are regularly used in equine athletes for the control of joint inflammation. OBJECTIVES The goal of this study was to utilise an acute synovitis inflammation model to determine the residual effects of IA betamethasone and triamcinolone acetonide on various inflammatory parameters and lameness. STUDY DESIGN Cross-over randomised trial. METHODS Five mixed-breed, 2-year-old horses were randomly allocated to an IA treatment of the radiocarpal joint with 9 mg of either betamethasone or triamcinolone acetonide. Two weeks following treatment, horses were injected with 1μg of lipopolysaccharide (LPS) diluted in 1 mL of saline. Following LPS injection, horses were crossed-over and both sets of injections repeated. Blood samples were collected at multiple time points for mRNA analysis, as well as serum amyloid A (SAA) and cortisol determination. At each time point, lameness was also subjectively scored. Additional injections with saline-only or LPS-only (twice) were conducted as negative and positive controls, respectively. Two-way repeated measures analysis of variance was used to analyse all data. RESULTS Corticosteroid-only treatments results in significant mRNA expression differences, as well as significant and prolonged cortisol suppression. Following LPS injection, there was a residual treatment effect with triamcinolone evidenced by a significant treatment effect on IL-6 and PTGS1 (cyclooxygenase-1), lameness, SAA, and cortisol concentrations, while only IL-6 expression was affected by betamethasone. MAIN LIMITATIONS The acute synovitis model used here results in significant inflammation and is not representative of the low-grade inflammation seen with typical joint disease and residual anti-inflammatory effects may be more profound in naturally-occurring joint disease. CONCLUSIONS Current regulatory guidelines may be insufficient if the concern is residual anti-inflammatory effects. Additionally, intra-articular corticosteroid administration is not without risk, as evidenced by a significant suppression of serum cortisol concentration and, as such, the benefits of their administration should be weighed against those risks. This article is protected by copyright. All rights reserved.