Selected Antimicrobial Information – Equine

Azithromycin [Equine]

Restriction Status



Species Usage Dose
For treatment of Rhodococcus equi 10mg/kg PO q24h; q48h treatment can be initiated after the first 5d of treatment (extra-label use)

Brand Name(s)



Azithromycin is a bacteriostatic, time-dependent macrolide antibiotic with broad-spectrum activity against Gram-positive aerobes and some Gram-negative aerobes, such as the Pasteurellaceae. Azithromycin is not effective against Pseudomonas aeruginosa, and many Enterobacteriaceae have acquired resistance. Azithromycin is bactericidal against Streptococcus spp. It is widely distributed and can be used to treat intracellular organisms and in the presence of necrotic tissue. Excretion is primarily in bile.

Acceptable Uses

  • Used in combination with rifampin for treatment of Rhodococcus equi pneumonia in foals.
  • Used in combination with rifampin for treatment of Streptococcus zooepidemicus pneumonia.
  • For treatment of internal abscesses.

Unacceptable Uses

  • N/A

Formulations Available within the OSU Pharmacy

  • Azithromycin 20mg/ml oral suspension
  • Azithromycin 250mg tablet


  • 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.


Icon for the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

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.