Macrolide-induced hyperthermia in foals: Role of impaired sweat responses.
Authors: Stieler A L, Sanchez L C, Mallicote M F, Martabano B B, Burrow J A, MacKay R J
Journal: Equine veterinary journal
Summary
# Editorial Summary: Macrolide-induced hyperthermia in foals Erythromycin, a macrolide antibiotic commonly used to treat foal gastric ulcer syndrome and other conditions, occasionally causes life-threatening hyperthermia in treated animals, yet the underlying mechanism has remained unclear. Stieler and colleagues conducted a blinded crossover study in ten healthy pony foals, administering either erythromycin (25 mg/kg orally three times daily) or placebo for ten days followed by ten days of pasture turnout, whilst measuring sweat responses using quantitative intradermal terbutaline injections on days 1, 3, 10 and 20. The erythromycin-treated foals demonstrated significantly impaired sweating across all post-baseline timepoints compared with controls, with rectal temperatures also significantly elevated (P=0.02), and notably six erythromycin-treated foals required hyperthermia treatment during initial turnout versus none in the control group. These findings indicate that erythromycin-induced anhidrosis—failure of normal thermoregulatory sweating—is the mechanism responsible for dangerous heat accumulation in susceptible foals. Practitioners prescribing macrolides should counsel clients on hyperthermia risk, monitor foals closely (particularly during or immediately after turnout), ensure adequate shade and hydration, and consider alternative antimicrobials where clinically appropriate, especially in warm weather or for foals with known risk factors.
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Practical Takeaways
- •Erythromycin use in foals carries a documented risk of life-threatening hyperthermia due to impaired sweating; monitor rectal temperature closely during and immediately after treatment
- •Foals receiving erythromycin should be managed in cool conditions and given frequent access to shade and water, especially during the first 10 days of treatment and subsequent turnout
- •Consider alternative antimicrobial agents when treating foals, or implement heightened surveillance protocols if erythromycin use is clinically necessary
Key Findings
- •Erythromycin treatment significantly reduced terbutaline-induced sweating in foals at all time-points compared to controls (P<0.05)
- •Peak rectal temperatures were significantly higher in erythromycin-treated foals than controls (P=0.02)
- •During the first 3 days after turnout, 6 erythromycin-treated foals required hyperthermia treatment versus 0 controls (P=0.03)
- •Drug-induced anhidrosis is identified as the likely mechanism of erythromycin-associated hyperthermia in foals