Macrolide-induced hyperthermia in foals: Role of impaired sweat responses.

This research article investigates the cause of heightened body temperature in young horses treated with erythromycin, and posits an impaired sweat response as the likely culprit.

Study Design and Methodology

• The researchers used a blind crossover study to investigate if erythromycin, a macrolide antibiotic, caused hyperthermia in foals by impairing sweat response.
• Ten healthy pony foals were housed in stalls and either received erythromycin or acted as controls over a period of 10 days, and were then set loose for another 10 days.
• To determine the sweat response, the researchers administered a terbutaline sweat test at four points during the study—Days 1 (as a baseline), 3, 10, and 20.
• Various statistical methods, like repeated-measures ANOVA with Bonferroni-corrected pairwise post hoc comparisons, Wilcoxon’s signed-rank test, and McNemar’s related samples test, were used to examine the effects of erythromycin, terbutaline, and duration of treatment on sweat response and temperature.

Findings of The Study

• The researchers found significant interaction between erythromycin and terbutaline in affecting sweat production in foals, especially after erythromycin treatment.
• Foals treated with erythromycin showed reduced sweating post-treatment compared to their baseline reading. This reduction was seen on forall days after discontinuation of erythromycin.
• Furthermore, erythromycin-treated foals were consistently found to produce lesser sweat than their control counterparts.
• Importantly, peak body temperatures were found to be significantly higher in erythromycin-treated foals when compared to controls. This was also supported by observations of more erythromycin-treated foals requiring treatment for hyperthermia during the first three days after being set loose.

Implications and Conclusions

• Based on the findings, the researchers concluded that erythromycin likely induces anhidrosis, inability to sweat, in foals, leading to the observed increase in body temperature (hyperthermia).
• This essential finding could help shape future erythromycin treatment protocols for foals and initiate a discussion on alternate antibiotics to minimize the risk of hyperthermia.