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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
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 →

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)
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 →

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.
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 →

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.
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 →

References

References

The PetCare.AI drug reference is built from 13 authoritative sources cited across 580 drug monographs.

Textbooks & handbooks — 5

  • Plumb's Veterinary Drug Handbook
  • Withrow & MacEwen's Small Animal Clinical Oncology
  • Merck Veterinary Manual
  • NRC Nutrient Requirements of Dogs and Cats
  • Veterinary Pharmacology and Therapeutics (Riviere & Papich)

Clinical guidelines & consensus — 4

  • ASPCA Animal Poison Control Center Guidelines
  • AAHA Diabetes Management Guidelines
  • ASPCA Poison Control Guidelines
  • RECOVER CPR Guidelines

Journals & peer-reviewed studies — 2

  • EPIC Study (J Vet Intern Med 2016)
  • JVIM FAT CAT Study

Regulatory & approvals — 1

  • CDSCO Veterinary Drug Approval Registry (1969–2026)

Databases — 1

  • Washington State University VCPL MDR1 Database

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
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