Selected Antimicrobial Information – Equine

Trimethoprim-Sulfonamide Combinations [Equine]

Restriction Status



Species Usage Dose

For treatment of susceptible infections 15-20mg/kg PO q12h
For treatment of lower respiratory tract infections cause by susceptible Streptococcus equi subsp. Zooepidemicus 15-20mg/kg PO q12h for 10d

Brand Name(s)

trimethoprim-sulfadiazine = Tribrissen®, trimethoprim-sulfamethoxazole = Bactrim®, Sulfatrim®, Bactrim DS®


Trimethoprim-sulfonamides are a group of time-dependent potentiated sulfonamide antibiotics. Sulfonamides are bacteriostatic when used alone, but bactericidal when used in combination with trimethoprim. They are broadly effective against many Gram-positive and Gram-negative aerobic bacteria, but are not effective against Pseudomonas spp., Mycoplasma spp., and most isolates of Klebsiella spp. In vivo activity against anaerobes is poor. Distribution is wide, and therapeutic concentrations can be achieved intracellularly and across the blood-brain barrier. Excretion is primarily in urine.

Acceptable Uses

  • Treatment of respiratory infections, septic arthritis, osteomyelitis, peritonitis, or meningitis. Culture/susceptibility are highly recommended to further guide treatment due to widespread resistance.
  • In combination with rifampin, for treatment of internal abscesses (despite poor penetration of purulent material when used alone).
  • Treatment of urinary tract infections.
  • Treatment of placentitis, retained fetal membranes, or epididymitis.

Unacceptable Uses

  • Inactivated in the presence of purulent or necrotic material (e.g. abscesses); recommended to use in combination with debridement or flushing.

Formulations Available within the OSU Pharmacy

  • Sulfamethoxazole/trimethoprim 400/80 tablet
  • Sulfamethoxazole/trimethoprim 800/160 tablet


  • Oral absorption may be decreased when given with food.


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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.