Effects of clarithromycin, azithromycin and rifampicin on terbutaline-induced sweating in foals.
Authors: Stieler Stewart A L, Sanchez L C, Mallicote M F, Muniz A L, Westerterp M S, Burrow J A, MacKAY R J
Journal: Equine veterinary journal
Summary
# Effects of Macrolide Antibiotics on Sweating in Foals Erythromycin is known to cause anhidrosis in foals, but the sweating effects of azithromycin and clarithromycin—macrolides frequently used alongside rifampicin to treat *Rhodococcus equi* pneumonia—remained unexplored until this 2017 investigation. Using quantitative intradermal terbutaline sweat testing, researchers administered various antimicrobial protocols orally for five days to groups of twelve foals, measuring sweat responses across multiple timepoints spanning 39 days post-treatment. All three macrolides suppressed sweating, though clarithromycin and azithromycin demonstrated considerably less potency than erythromycin; rifampicin alone had no effect on sweat output, and whilst it marginally reduced erythromycin-induced anhidrosis on day one of treatment, this protective effect did not persist. For equine practitioners treating foals with *R. equi* infection, these findings indicate that any macrolide selection (erythromycin, azithromycin, or clarithromycin) carries risk of inducing anhidrosis, with important implications for thermoregulation during treatment and recovery—a particular concern in febrile foals where impaired sweating capacity could compromise heat dissipation and complicate clinical management.
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Practical Takeaways
- •Expect anhidrosis (impaired sweating) in foals treated with any macrolide antibiotic (erythromycin, azithromycin, clarithromycin) for Rhodococcus equi pneumonia; monitor closely during exercise and hot weather to prevent heat stress
- •Azithromycin and clarithromycin are safer alternatives to erythromycin if sweating capacity is a concern, though both still cause some sweat suppression
- •Adding rifampicin to erythromycin does not significantly protect against anhidrosis and should not be relied upon to mitigate this side effect
Key Findings
- •All three macrolides (erythromycin, azithromycin, clarithromycin) suppressed sweating in foals, with erythromycin being most potent
- •Clarithromycin and azithromycin induced less sweat suppression than erythromycin
- •Rifampicin alone had no effect on sweating but slightly reduced erythromycin-induced anhidrosis on Day 1 of treatment only
- •Macrolide-induced anhidrosis persisted through the 39-day observation period despite concurrent rifampicin administration