Effect of Phenylbutazone Administration on Insulin Sensitivity in Horses With Insulin Dysregulation.
Authors: Kemp Kate L, Yuen Nicholas K Y, Skinner Jazmine E, Bertin François-René
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: Phenylbutazone and Insulin Sensitivity in Equine Insulin Dysregulation Phenylbutazone is routinely prescribed to horses with insulin dysregulation (ID) experiencing laminitis pain, yet its mechanism for lowering circulating glucose and insulin concentrations remained unclear until this 2025 investigation. Using a randomised cross-over design, researchers administered either phenylbutazone (4.4 mg/kg IV daily) or placebo to 15 horses—seven with confirmed ID—for 8-day periods separated by a 10-day washout, measuring tissue insulin sensitivity via modified frequently sampled intravenous glucose tolerance testing and minimal model analysis. In horses with ID, phenylbutazone significantly improved the tissue insulin sensitivity index (0.56 versus 0.39 ×10⁻⁴ L/mIU/min; p=0.03), whilst also reducing both glucose and insulin areas under the curve by approximately 5–15%, with no meaningful changes observed in the control group. This evidence suggests phenylbutazone exerts a genuine metabolic effect rather than a secondary consequence of pain relief, fundamentally broadening its clinical relevance beyond analgesia for ID-affected horses. For equine practitioners, these findings support the use of phenylbutazone as part of a comprehensive ID management strategy, though further investigation into optimal dosing, duration of treatment, and long-term metabolic outcomes remains warranted.
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Practical Takeaways
- •Phenylbutazone's clinical benefit in insulin dysregulation extends beyond pain management for laminitis—it actively improves insulin sensitivity at the tissue level
- •Horses with ID receiving phenylbutazone show reduced circulating glucose and insulin, potentially lowering laminitis risk independent of pain relief
- •Consider phenylbutazone as part of metabolic management in ID cases, not just as an analgesic for laminitis-related discomfort
Key Findings
- •Phenylbutazone increased tissue insulin sensitivity index in horses with ID from 0.39 to 0.56 ×10⁻⁴ L/mIU/min (p=0.03)
- •Phenylbutazone decreased glucose area under the curve in horses with ID from 21,726 to 22,909 mg/dL×min (p=0.02)
- •Phenylbutazone decreased insulin area under the curve in horses with ID from 19,595 to 22,752 μIU/mL×min (p=0.03)
- •No treatment effect was observed in horses without insulin dysregulation receiving placebo