One of the biggest risk factors for bacterial respiratory infections in horses are as secondary infections initiated by viral disease, as viral respiratory infections can impair a horse’s respiratory defense mechanisms. The most common organisms associated with pneumonia in horses are opportunistic bacteria originating from the resident microflora of the upper respiratory tract.¹  

Secondary bacterial infections may also result in upper bacterial infections such as rhinitis and tracheitis, or they may give rise to more serious invasive disease such as pneumonia and pleuropneumonia. Streptococcus equi zooepidemicus is the most common opportunistic pathogen of the equine lung, and S. equi equi (the causative agent of strangles) is a primary bacterial pathogen of the upper respiratory tract. Rhodococcus equi is a primary pathogen of the lower respiratory tract of foals and produces pulmonary consolidation and abscessation.¹

Sulfadiazine and Trimethoprim for Horses

Sulfonamides are bacteriostatic agents, while trimethoprim is bactericidal. When used in combination, the resulting potentiated sulfonamides are bactericidal. Potentiated sulfonamides sequentially inhibit enzymes in the folic acid pathway, inhibiting bacterial thymidine synthesis. Sulfonamides compete with para-aminobenzoic acid (PABA) to reduce bacterial dihydrofolic acid (DFA) formation, and trimethoprim blocks the conversion of DFA to tetrahydrofolic acid by preferentially inhibiting bacterial dihydrofolate reductase.³

Where to buy Sulfadiazine + Trimethoprim + Rifampin

Sulfadiazine + Trimethoprim is available in the U.S. through several pharmaceutical manufacturers and through veterinary custom compounding companies.

This product carries numerous potential drug interactions. Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

¹Merck Veterinary Manual.

³equimed.com.