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  Discussion on Macrolide Induced Hyperthermia in Foals
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DrO

Posted on Saturday, Jul 18, 2015 - 3:43 pm:

A long observed phenomena appears to have been explained. For more on this, prevention, and treatment see the article. Surprisingly the problem persisted for longer than 20 days.
DrO

Equine Vet J. 2015 Jul 14.
Macrolide-induced hyperthermia in foals: Role of impaired sweat responses.

Stieler AL1, Sanchez LC1, Mallicote MF1, Martabano BB1, Burrow JA1, MacKay RJ1.

Author information:
1Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, PO Box 100136, Gainesville, FL, 32610, USA.

Abstract
REASONS FOR PERFORMING STUDY:
The mechanism of hyperthermia, a potentially fatal adverse effect of erythromycin treatment of foals, is unknown.

OBJECTIVES:
To determine the cause of erythromycin-associated hyperthermia. It was hypothesised that the normal sweat response of foals is impaired by treatment with erythromycin.

STUDY DESIGN:
Blinded, crossover study in 10 healthy pony foals.

METHODS:
Foals kept in stalls were given either erythromycin (25 mg/kg bwt orally, 3 times daily) or control for 10 days then turned out for a further 10 days. Quantitative intradermal terbutaline sweat tests were performed on Days 1 (baseline), 3, 10 and 20. The effects on terbutaline-induced sweating of erythromycin, terbutaline concentration, and treatment day were analysed by repeated-measures ANOVA with Bonferroni-corrected pairwise post hoc comparisons. Peak temperatures were compared by Wilcoxon Signed Rank and proportions by McNemar's Related Samples tests. Significance was set at P<0.05.

RESULTS:
There were significant 2-factor interactions for treatment × terbutaline after baseline, treatment × day at every terbutaline concentration, and day × terbutaline for erythromycin (P<0.001) but not control (P = 0.9) treatment. Sweating was significantly reduced from baseline in erythromycin-treated foals at all subsequent days. Erythromycin-treated foals produced less sweat at all time-points compared to control-treated foals (P<0.05). Peak rectal temperatures of erythromycin-treated foals were significantly higher (P = 0.02) than those of controls. During the first 3 days outside more erythromycin- compared to control-treated foals required treatment for hyperthermia (6 vs. 0; P = 0.03).

CONCLUSIONS:
We believe drug-induced anhiDrOsis is the likely cause of hyperthermia in some foals treated with erythromycin
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