Equine · Equus caballus · typical adult weight 350.00–700.00 kg
Trimethoprim-Sulfamethoxazole is dosed at 24 mg/kg PO q12h for 10 days in horses, per Plumb's Veterinary Drug Handbook, 9th Ed, p.1223 (Sulfa-/Trimethoprim, Dosages, HORSES) — EDITION NOTE 2026-08-06: this rule's Plumb's reference names the 9th edition, which is not held and was never consulted. The held copy is the 10th ed (2023). The Plumb's line was never confirmed against the held edition, so rely on it only as background; any other source named in this citation is unaffected. — LOCATOR CONVENTION 2026-08-07: the bare 'p.1223' in this citation is the PDF index of the held scan, not the printed page. The PRINTED page is p.1196; verified by finding the drug named there. If you are holding the book, turn to p.1196. — SOURCE EDITION: Plumb's Veterinary Drug Handbook — ISBN 9781394172207, https://openlibrary.org/isbn/9781394172207. Trimethoprim-Sulfamethoxazole is used in horses for Severe bacterial infection, Susceptible bacterial infections, Bacterial infection. Routes documented in horses: PO. A typical adult horse weighs 350.00–700.00 kg. ExoticRx lists 3 cited dose rules for Trimethoprim-Sulfamethoxazole in horses, drawn from published veterinary references. Verify against current literature before clinical use.
US trade names: Bactrim, TMS
| Route | Dose | Frequency | Duration | Indication | Evidence | Source |
|---|---|---|---|---|---|---|
| PO | 24 mg/kg | q12h for 10 days | 5-7 days | Severe bacterial infection | Moderate | Plumb's Veterinary Drug Handbook, 9th Ed, p.1223 (Sulfa-/Trimethoprim, Dosages, HORSES) — EDITION NOTE 2026-08-06: this rule's Plumb's reference names the 9th edition, which is not held and was never consulted. The held copy is the 10th ed (2023). The Plumb's line was never confirmed against the held edition, so rely on it only as background; any other source named in this citation is unaffected. — LOCATOR CONVENTION 2026-08-07: the bare 'p.1223' in this citation is the PDF index of the held scan, not the printed page. The PRINTED page is p.1196; verified by finding the drug named there. If you are holding the book, turn to p.1196. — SOURCE EDITION: Plumb's Veterinary Drug Handbook — ISBN 9781394172207, https://openlibrary.org/isbn/9781394172207 |
| PO | 24–30 mg/kg | q12h | 7-14 days | Susceptible bacterial infections | Strong | EQUISUL-SDT - Sulfadiazine and Trimethoprim Suspension [US Product Label for Horses]. Aurora Pharmaceutical, Inc.; 2021. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=434cfb08-bb19-46fc-a55d-b9ecf0bec601; Winther L, Guardabassi L, Baptiste KE, Friis C. Antimicrobial disposition in pulmonary epithelial lining fluid of horses. Part I. Sulfadiazine and trimethoprim. J Vet Pharmacol Ther. 2011;34(3):277-284. doi:10.1111/j.1365-2885.2010.01229.x — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.1223 (2026-08-01). — LOCATOR CONVENTION 2026-08-07: the bare 'p.1223' in this citation is the PDF index of the held scan, not the printed page. The PRINTED page is p.1196; verified by finding the drug named there. If you are holding the book, turn to p.1196. — SOURCE EDITION: Plumb's Veterinary Drug Handbook — ISBN 9781394172207, https://openlibrary.org/isbn/9781394172207 |
| PO | 24–30 mg/kg | q12h | 7-14 days | Bacterial infection | Strong | EQUISUL-SDT - Sulfadiazine and Trimethoprim Suspension [US Product Label for Horses]. Aurora Pharmaceutical, Inc.; 2021. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=434cfb08-bb19-46fc-a55d-b9ecf0bec601; Winther L, Guardabassi L, Baptiste KE, Friis C. Antimicrobial disposition in pulmonary epithelial lining fluid of horses. Part I. Sulfadiazine and trimethoprim. J Vet Pharmacol Ther. 2011;34(3):277-284. doi:10.1111/j.1365-2885.2010.01229.x — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.1223 (2026-08-01). — LOCATOR CONVENTION 2026-08-07: the bare 'p.1223' in this citation is the PDF index of the held scan, not the printed page. The PRINTED page is p.1196; verified by finding the drug named there. If you are holding the book, turn to p.1196. — SOURCE EDITION: Plumb's Veterinary Drug Handbook — ISBN 9781394172207, https://openlibrary.org/isbn/9781394172207 |
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These ranges are per kg. Enter your horse's weight to get the precise dose and draw-up volume — unit and concentration math done for you.
Sequential blockade of folate synthesis: sulfamethoxazole inhibits dihydropteroate synthase; trimethoprim inhibits dihydrofolate reductase.
May cause keratoconjunctivitis sicca (KCS) in dogs with prolonged use. Can cause bone marrow suppression. Avoid in animals with hepatic disease. Adequate hydration required.
Species-specific contraindications and adverse-reaction reports for horses may differ from canine / feline reference data — consult the primary citations listed with each rule.
Trimethoprim-Sulfamethoxazole dose ranges in horses, with cited source references: PO 24 mg/kg q12h for 10 days; PO 24–30 mg/kg q12h; PO 24–30 mg/kg q12h. Reference ranges from cited sources — verify against current literature before clinical use.
Documented routes for Trimethoprim-Sulfamethoxazole in horses: PO.
Cited course lengths for Trimethoprim-Sulfamethoxazole in horses include: 5-7 days; 7-14 days. Duration depends on the indication — match it to the specific dose rule in the table above.
Trimethoprim-Sulfamethoxazole is indicated in horses for: Severe bacterial infection, Susceptible bacterial infections, Bacterial infection.
These are general warnings for Trimethoprim-Sulfamethoxazole across species; consult the horse dosing table above for species-specific guidance. May cause keratoconjunctivitis sicca (KCS) in dogs with prolonged use. Can cause bone marrow suppression. Avoid in animals with hepatic disease. Adequate hydration required.
Why a species-specific page? Trimethoprim-Sulfamethoxazole pharmacokinetics differ across species: dose ranges, intervals, and route preferences are not interchangeable. Cross-extrapolation from canine doses is unsafe in horses — the rules above are the citations specific to this species, not generic recommendations.
Sourced from published veterinary references; awaiting credentialed clinical reviewer. See our editorial process. Reference only — not veterinary advice.