Selected Antimicrobial Information – Equine

Doxycycline [Equine]

Restriction Status



Species Usage Dose

For treatment of Lyme disease 10mg/kg PO q12h for 1-2mos
For treatment of anaplasmosis 10mg/kg PO q12h for10-14d
For treatment of organisms with MIC ≤ 0.25mcg/mL 10mg/kg PO q24h
For treatment of organisms with MIC 0.5-1.0mcg/mL 10mg/kg PO q12h

Brand Name(s)



Doxycycline is a bacteriostatic, time-dependent tetracycline antibiotic with a broad spectrum of activity against many Gram-positive and Gram-negative aerobes. It is not effective against Proteus spp. or Pseudomonas spp. There is activity against some anaerobes, but efficacy against Clostridium spp. is variable. Intracellular organisms are highly susceptible. Distribution is wide, and it is the only tetracycline that effectively crosses the blood-brain barrier. Doxycycline is primarily excreted in feces.

Acceptable Uses

  • As an oral alternative to oxytetracycline for the treatment of anaplasmosis, Potomac Horse Fever, Lyme Disease, or leptospirosis.
  • As an alternative therapy for lower respiratory disease in foals caused by β-hemolytic Streptococcus spp. or Rhodococcus equi.

Unacceptable Uses

  • Should never be given IV.

Formulations Available within the OSU Pharmacy

  • Doxycycline 50mg capsule
  • Doxycycline 100mg capsule
  • Doxycycline 20mg tablet
  • Doxycycline 100mg tablet
  • Vibramycin 10mg/ml oral suspension
  • Vibramycin 50mg/5ml syrup


  • Bioavailability of doxycycline is greater in foals than adult horses; doses exceeding 10mg/kg should only be used in adult horses, and there is increased risk of diarrhea with increasing dose.
  • Doxycycline should not be given parenterally to horses because of unknown safety.


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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.