Systemic absorption of triamcinolone acetonide is increased from intrasynovial versus extrasynovial sites and induces hyperglycemia, hyperinsulinemia, and suppression of the hypothalamic-pituitary-adrenal axis.
Authors: Hallowell Kimberly L, Dembek Katarzyna, Horne Caitlyn R, Knych Heather K, Messenger Kristen M, Schnabel Lauren V
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: Triamcinolone Absorption and Metabolic Effects in Horses The risk of steroid-associated laminitis following therapeutic joint injections remains poorly understood, with injection site location and pre-existing metabolic status potentially influencing outcomes. Researchers administered 18 mg triamcinolone acetonide (TA) bilaterally to 20 horses via either intrasynovial (antebrachiocarpal) or extrasynovial (sacroiliac) injection, collecting blood samples over 72 hours to measure drug absorption and metabolic markers including glucose, insulin, cortisol, and ACTH. Peak plasma TA concentrations occurred at 8 hours post-injection, but intrasynovial injections produced significantly higher systemic absorption (1.397 ng/mL versus 0.672 ng/mL), with elevated levels persisting until 36 hours. Both groups developed hyperglycaemia and hyperinsulinaemia from 1–72 hours post-injection regardless of injection site; critically, horses with baseline insulin exceeding 20 µU/mL experienced marked hyperinsulinaemia (mean peak 197.5 µU/mL) compared to metabolically normal horses (90.06 µU/mL), whilst cortisol and ACTH were suppressed from 4–72 hours in both groups. For practitioners, these findings suggest that pre-injection metabolic screening—particularly identifying horses with elevated baseline insulin—should inform risk stratification for steroid-associated laminitis, and that intrasynovial injections warrant closer post-injection monitoring than sacroiliac approaches given their substantially higher systemic bioavailability.
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Practical Takeaways
- •Intrasynovial joint injections (carpal) produce higher systemic steroid absorption than extrasynovial injections (sacroiliac), potentially increasing laminitis risk—consider extrasynovial sites when possible, particularly in at-risk horses
- •Screen horses for elevated baseline insulin (>20 μU/mL) before corticosteroid injection; horses with pre-existing insulin dysregulation experience severe hyperinsulinemia post-injection and warrant closer monitoring for laminitis
- •Expect significant metabolic changes for 48-72 hours post-injection regardless of site; combine corticosteroid use with aggressive laminitis prevention (controlled movement, substrate management, potential prophylactic medication) especially in horses with endocrinopathies
Key Findings
- •Intrasynovial (antebrachiocarpal) injection of triamcinolone acetonide resulted in significantly higher peak plasma levels (1.397 ng/mL at 8h) compared to extrasynovial (sacroiliac) injection (0.672 ng/mL), with sustained elevation from 8-36h post-injection
- •Triamcinolone acetonide induced hyperglycemia (elevated from 1-72h) and hyperinsulinemia (elevated from 10-72h) in all horses, with horses having baseline insulin >20 μU/mL experiencing marked hyperinsulinemia peaking at 197.5 μU/mL versus 90.06 μU/mL in normal baseline insulin horses
- •Both injection sites suppressed hypothalamic-pituitary-adrenal axis function, with cortisol and ACTH significantly decreased from 4-72h post-injection
- •Baseline endocrinopathies appear to amplify corticosteroid-induced metabolic derangements, suggesting pre-existing insulin dysregulation may be a risk factor for steroid-associated laminitis