Macrolide‐induced hyperthermia in foals: Role of impaired sweat responses

Abstract

We believe drug-induced anhidrosis is the likely cause of hyperthermia in some foals treated with erythromycin.

Effects of clarithromycin, azithromycin and rifampicin on terbutaline‐induced sweating in foals

“…Consistent with the results of our previous study , ERY treatment suppressed sweating during and after treatment. Erythromycin‐induced anhidrosis is the likely explanation for reports of hyperthermia in foals treated for R. equi pneumonia with this antibiotic .…”

“…Because foals in the current study were protected from direct sunlight for 5 days after treatment regimens were completed, signs of heat stress attributable to treatment were not seen. In the previous study, six of 10 foals that were given ERY then immediately moved outside developed signs of heat stress within 3 days whereas only one of 24 ERY‐treated foals in the current experiment became hyperthermic during the first 3 days after turnout .…”

Clinical Approach to Commonly Encountered Problems

“…20,23 In Quarter Horses and American Paint Horses, MH is inherited as an autosomal dominant trait that is linked to a single point mutation in the skeletal muscle ryanodine receptor 1 (RyR1) gene at nucleotide C7360G. 28,29 Erythromycin causes a drug-induced anhidrosis that is the likely cause of the hyperthermia. Horses with polysaccharide storage myopathy tend to have a more severe clinical phenotype if they are concurrently affected with the MH mutation.…”

“…23,24 This mutation can be identified by genetic testing. 29 Because the sweat response of treated foals is impaired, these foals are at particular risk of hyperthermia when exposed to hot, humid environments and direct sunlight. 24 Central Nervous System.…”

“…256,[279][280][281] The receptors are generally widely expressed in the lung, although the pattern of specific receptor expression can vary among species. [28][29][30] However, direct sympathetic innervation of airway smooth muscle is minimal to none, and thus stimulation of the adrenergic receptors is primarily via circulating catecholamines. Vagal-mediated parasympathetic stimulation is important in the regulation of airway smooth muscle tone, and stimulation can cause bronchoconstriction as well as mucus secretion and bronchial vasodilation.…”