Selected Antimicrobial Information – Equine

Erythromycin [Equine]

Restriction Status



Species Usage Dose
For treatment of Rhodococcus equi in foals 20-25mg/kg PO q8h (extra-label use)
For treatment of Lawsonia intracellularis in foals 25mg/kg PO q6-8h (extra-label use)

10mg/kg PO q12h when used with rifampin (extra-label use)

Brand Name(s)



Erythromycin is a concentration-dependent, primarily bacteriostatic macrolide antibiotic. It may be bactericidal at high doses. Erythromycin is active against Gram-positive aerobes. There is also some efficacy against non-enteric Gram-negatives such as Actinobacillus spp. and Pasteurella spp., and anaerobes such as Clostridium spp. and Fusobacterium spp. Distribution throughout the body is wide, and excretion is primarily in bile. .

Acceptable Uses

  • Treatment of Rhodococcus equi pneumonia in foals when used in combination with rifampin.
  • Treatment of Lawsonia intracellularis (equine proliferative enteropathy) in foal; used with or without rifampin.

Unacceptable Uses

  • N/A

Formulations Available within the OSU Pharmacy

  • Currently no oral erythromycin formulations available within the OSU pharmacy; available upon request


  • Severe and fatal colitis has been associated with macrolide use in adult horses and thus should be avoided in adults. Foals receiving treatment with a macrolide antibiotic should have their mouths rinsed out after to administration to prevent adverse effects to the mare.
  • Macrolides have been associated with significant hyperthermia in treated foals due to off-target effects on apocrine sweat glands; treated foals should not be housed in direct sunlight for prolonged periods of time and should have access to a climate-controlled enclosure.


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OSU VMC Antimicrobial Use Guidelines Copyright © 2018 by The Ohio State University College of Veterinary Medicine is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.