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Sulfa-Trimethoprim (TMP-Sulfa)

Prescription
Potentiated Sulfonamide Antibiotic
Last reviewed 22 Apr 2026 · PetCare.AI Editorial Team
Species
Dog, Cat
Brands
3 available
Interactions
1 documented
Formulations
3

Mechanism of action

Sequential inhibition of folate synthesis: sulfonamide inhibits dihydropteroate synthase (DHPS) and trimethoprim inhibits dihydrofolate reductase (DHFR). Combined, they are synergistically bactericidal despite each being bacteriostatic alone. 1:5 TMP:sulfa ratio.

At a glance

Class
Potentiated Sulfonamide Antibiotic
Schedule
Prescription
Storage
Store at room temperature, protect from light

Dosing

🐕

Dog

Broad-spectrum antibiotic for UTIs, skin infections, prostatitis (excellent pene
Dose
15–30 mg/kg
Route
PO, IV
Frequency
q12h
🐈

Cat

Used for UTIs, toxoplasmosis (with pyrimethamine), and skin infections
Dose
15 mg/kg
Route
PO
Frequency
q12h

Formulations

💊

Other — 3

Strength
—
Strength
—
Strength
—

Storage

Store at room temperature, protect from light

Safety

Monitoring parameters

Schirmer tear test q2–4 weeks (KCS prevention)CBC every 2 weeks initially (myelosuppression)Urinalysis (crystalluria — ensure hydration)Hepatic enzymesThyroid function with chronic use (>6 weeks)

Interactions

Major — 1

Azathioprine
major
Both cause myelosuppression via folate pathway interference. Combined: severe bone marrow suppression risk.
Management: Avoid. Use amoxicillin or cephalosporin instead of TMP-sulfa during azathioprine therapy.

Brands

Other markets

Tribrissen
Bactrim
Septra

FAQs

Frequently asked questions

›What is Sulfa-Trimethoprim (TMP-Sulfa)?
Sulfa-Trimethoprim (TMP-Sulfa) is a potentiated sulfonamide antibiotic used in pets. Sequential inhibition of folate synthesis: sulfonamide inhibits dihydropteroate synthase (DHPS) and trimethoprim inhibits dihydrofolate reductase (DHFR). Combined, they are synergistically bactericidal despite each being bacteriostatic alone. 1:5 TMP:sulfa ratio.
›What is Sulfa-Trimethoprim (TMP-Sulfa) used for in pets?
Sulfa-Trimethoprim (TMP-Sulfa) is used in veterinary medicine for: Broad-spectrum antibiotic for UTIs, skin infections, prostatitis (excellent pene; Used for UTIs, toxoplasmosis (with pyrimethamine), and skin infections.
›What is the Sulfa-Trimethoprim (TMP-Sulfa) dose for dogs?
For dogs, Sulfa-Trimethoprim (TMP-Sulfa) is typically dosed as follows — Broad-spectrum antibiotic for UTIs, skin infections, prostatitis (excellent pene: 15–30 mg/kg PO/IV q12h. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›What is the Sulfa-Trimethoprim (TMP-Sulfa) dose for cats?
For cats, Sulfa-Trimethoprim (TMP-Sulfa) is typically dosed as follows — Used for UTIs, toxoplasmosis (with pyrimethamine), and skin infections: 15 mg/kg PO q12h. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.
›Does Sulfa-Trimethoprim (TMP-Sulfa) need a prescription?
Yes. Sulfa-Trimethoprim (TMP-Sulfa) is a prescription medication and should only be administered under veterinary supervision.

References

References

Textbooks & handbooks

  • Plumb, D.C. Plumb's Veterinary Drug Handbook. 10th ed., Wiley-Blackwell, 2023.
  • Vail, D.M., Thamm, D.H., & Liptak, J.M. (eds.). Withrow & MacEwen's Small Animal Clinical Oncology. 6th ed., Saunders/Elsevier, 2020.
  • Riviere, J.E., & Papich, M.G. (eds.). Veterinary Pharmacology and Therapeutics. 10th ed., Wiley-Blackwell, 2018.
  • National Research Council. Nutrient Requirements of Dogs and Cats. National Academies Press, Washington DC, 2006.
  • The Merck Veterinary Manual. Merck & Co., Online edition. https://www.merckvetmanual.com/

Clinical guidelines & consensus

  • Fletcher, D.J., Boller, M., Brainard, B.M., et al. "RECOVER Evidence and Knowledge Gap Analysis on Veterinary CPR." Journal of Veterinary Emergency and Critical Care, 2012;22(S1):S102–S131.
  • American Animal Hospital Association. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. AAHA Press.

Journals & peer-reviewed studies

  • Hogan, D.F., Fox, P.R., Jacob, K., et al. "Secondary prevention of cardiogenic arterial thromboembolism in the cat: The FAT CAT study." Journal of Veterinary Cardiology, 2015;17(Suppl 1):S306–S317.
  • Boswood, A., Häggström, J., Gordon, S.G., et al. "Effect of Pimobendan in Dogs with Preclinical Myxomatous Mitral Valve Disease and Cardiomegaly: The EPIC Study — A Randomized Clinical Trial." Journal of Veterinary Internal Medicine, 2016;30(6):1765–1779.
  • ASPCA Animal Poison Control Center. Toxicology and Poison Management Guidelines. American Society for the Prevention of Cruelty to Animals. https://www.aspca.org/pet-care/animal-poison-control

Regulatory & approvals

  • Central Drugs Standard Control Organisation (CDSCO), Government of India. Veterinary Drug Approval Registry, 1969–2026. Directorate General of Health Services. https://cdsco.gov.in/

Databases

  • Washington State University, College of Veterinary Medicine. Veterinary Clinical Pharmacology Laboratory (VCPL) — MDR1 Multidrug Sensitivity Database. https://vcpl.vetmed.wsu.edu/
Educational reference only
This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →

Related medicines

Other medicines in the same class (Potentiated Sulfonamide Antibiotic).

Sulfadimethoxine/Ormetoprim
Rx
Synergistic combination: sulfadimethoxine inhibits DHPS and ormetoprim inhibits DHFR (same sequential folate blockade as TMP-sulfa). Long half-life allows once-daily dosing. FDA-approved for dogs.
dogcat
Trimethoprim-Sulfamethoxazole
Rx
Sequential blockade of folate synthesis — sulfamethoxazole inhibits dihydropteroate synthase, trimethoprim inhibits dihydrofolate reductase
dogcat