Trimethoprim / Sulfadiazine (TMP-Sulfa): veterinary dose and monograph

At a glance

Drug class

Antibiotic

Also known as

Tribrissen, Bactrim, TMP-S, Cotrimoxazole

Species with doses

Dogs, Cats, Cattle, Horses, Pigs, Birds, Rabbits, Ferrets, Guinea pigs, Reptiles, Chinchillas, Rats and Primates

General dose range

15–30 mg/kg PO q12h — check the species tables for the indication

Routes

PO, IV, IM

Last reviewed

1 October 2026

Indications

• UTI (susceptible E. coli, Proteus, Staphylococcus)
• Pyoderma / skin & soft tissue infection
• Respiratory infection (CIRDC, BRD)
• Prostatitis (good prostate penetration vs many other antibiotics)
• Coccidiosis (Isospora, Eimeria)
• Pneumocystis carinii pneumonia (immunosuppressed)
• Toxoplasmosis (alternative to clindamycin)

Trimethoprim / Sulfadiazine (TMP-Sulfa) dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• UTI / pyoderma / soft tissue: Doses are trimethoprim + sulfonamide combined. Papich 5e: 15 mg/kg q12h PO or 30 mg/kg q12–24h PO. Plumb’s p.1089 (Greene 2006): UTI/pyoderma 30 mg/kg PO q24h (not soft-tissue infections) or 15 mg/kg q12h for 14 days; bacterial UTI 30 mg/kg q12h (Bartges 2007). Watch for KCS, polyarthropathy and hypersensitivity (Dobermans predisposed).
• Pneumocystis carinii pneumonia: Plumb’s p.1089 (Hawkins 2000): 15 mg/kg PO q8h OR 30 mg/kg PO q12h, both for 3 weeks. (The previous 30 mg/kg q6h doubled the reference daily dose.)
• Toxoplasmosis / Neospora: Papich 5e: Toxoplasma 30 mg/kg q12h PO. Plumb’s p.1089 (Lappin 2000): toxoplasmosis 15 mg/kg PO q12h for 28 days; Neospora 15 mg/kg PO q12h for 4 weeks with clindamycin 10 mg/kg q12h or pyrimethamine 1 mg/kg once daily; 15–30 mg/kg twice daily with pyrimethamine (Blagburn 2005).

Cats

• Susceptible infection: Papich 5e: 15 mg/kg q12h PO or 30 mg/kg q12–24h PO. Plumb’s p.1089: UTI 30 mg/kg PO q24h or 15 mg/kg q12h for 7–14 days (Greene 2006); toxoplasmosis 15 mg/kg q12h for 28 days (Lappin 2000a). Tablets are bitter — cats often salivate.

Cattle

• Susceptible infection (extra-label): Plumb’s p.1089: cattle 25 mg/kg IV or IM q24h (Burrows 1980); 44 mg/kg once daily IM or IV (Upson 1988). Papich 5e: trimethoprim is not absorbed orally in ruminants (it is in calves); trimethoprim-sulfadoxine has been used at 16 mg/kg q24h IV or IM. No approved US cattle product — obtain a FARAD withdrawal.
• Calves — susceptible infection (extra-label): Plumb’s p.1089 (Baggot 1983): calves 48 mg/kg IV or IM q24h. Extra-label — obtain a FARAD withdrawal.

Horses

• Susceptible infection: Papich 5e: label oral-suspension dose 24 mg/kg (20 mg/kg sulfadiazine + 4 mg/kg trimethoprim) q12h for 10 days; many clinicians use 25–30 mg/kg q12h PO. Plumb’s p.1089: 15–30 mg/kg PO q12h, 30 min before hay (Foreman 1999); foals 30 mg/kg PO q12h or 15 mg/kg IV q12h.
• EPM (Sarcocystis neurona): Potentiated sulfonamide given with pyrimethamine 1 mg/kg PO once daily for 90–120 days or longer (Plumb’s pyrimethamine monograph, MacKay 2000). Monitor CBCs — leukopenia, thrombocytopenia and anaemia occur; folinic acid or yeast may help. Combined TMP-sulfa dose: Papich 5e label 24 mg/kg q12h, clinicians 25–30 mg/kg q12h PO.

Pigs

• Susceptible infection: Plumb’s p.1089 (Baggot 1983): swine 48 mg/kg (combined) IM q24h. Extra-label — obtain a withdrawal (FARAD).

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• Susceptible infection (extra-label): Plumb’s p.1089: cattle 25 mg/kg IV or IM q24h (Burrows 1980); 44 mg/kg once daily IM or IV (Upson 1988). Papich 5e: trimethoprim is not absorbed orally in ruminants (it is in calves); trimethoprim-sulfadoxine has been used at 16 mg/kg q24h IV or IM. No approved US cattle product — obtain a FARAD withdrawal.
• Calves — susceptible infection (extra-label): Plumb’s p.1089 (Baggot 1983): calves 48 mg/kg IV or IM q24h. Extra-label — obtain a FARAD withdrawal.

Birds

• Psittacines — susceptible infection: Plumb’s p.1089: oral suspension 50–100 mg/kg (combined) PO q12h (Hoeffer 1995); 2 mL/kg of the 240 mg/5 mL suspension PO twice daily (McDonald 1989) — may cause emesis in macaws. Not for laying hens (egg residues).

Rabbits

• Susceptible infection (oral): Plumb’s p.1089 (Ivey & Morrisey 2000): rabbits 15–30 mg/kg PO q12–24h, or 30–48 mg/kg SC q12h. Sulfadiazine has a very short half-life (about 1 h) in rabbits.

Ferrets

• Susceptible infection: Plumb’s p.1089: 30 mg/kg PO twice daily (Williams 2000); coccidiosis 30 mg/kg PO once daily for 14 days (Johnson 2006).

Guinea pigs

• Susceptible infection: Plumb’s p.1089 (Adamcak & Otten 2000): chinchillas, gerbils, guinea pigs, hamsters, mice and rats 15–30 mg/kg PO q12h, or 30 mg/kg IM q12h.

Reptiles

• Susceptible infection: Plumb’s p.1089: most species 30 mg/kg IM (cranial half of body) once daily for 2 doses, then every other day for 5–12 treatments (Gauvin 1993; Jacobson 1999); 15–25 mg/kg/day IM for 7–14 days (Lewbart 2001). Keep the reptile well hydrated.

Chinchillas

• Susceptible infection: Plumb’s p.1089: 15–30 mg/kg PO q12h or 30 mg/kg IM q12h (Adamcak & Otten 2000); 30 mg/kg PO, SC or IM q12h (Hayes 2000).

Rats

• Susceptible infection: Plumb’s p.1089 (Adamcak & Otten 2000): 15–30 mg/kg PO q12h or 30 mg/kg IM q12h.

Primates

• Susceptible infection (prosimians): Carpenter Exotic Animal Formulary 6th ed, Table 13-1 (p.680, 684): prosimians 30 mg/kg PO/IM q24h (combined); marmosets/capuchins/lemurs (trimethoprim/sulfadiazine) 15 mg/kg PO q12h or 30 mg/kg SC/IM q24h.

Contraindications

Hypersensitivity to sulfonamides. Hepatic parenchymal damage, blood dyscrasias. Sight-hound breed history of sulfa hypersensitivity (Doberman). Pregnancy in food animals — folate antagonism, last trimester. KCS / Sjogren's history (sulfa can precipitate dry eye in dogs). Severe renal disease (crystalluria risk — ensure good hydration).

Species-specific warnings

Dogs: KCS risk — Schirmer test baseline + monthly. Doberman idiosyncratic hypersensitivity. Hypothyroidism with prolonged use.

Horses: EPM treatment workhorse. 24–30 mg/kg PO q12h. Folate supplementation for >3 weeks.

Cattle: Extra-label use; 16 d slaughter / 4 d milk withdrawal verified by FARAD.

Adverse effects

• KCS (keratoconjunctivitis sicca) in dogs — DO SCHIRMER TEST at 14 days and monthly during chronic therapy
• Hypersensitivity — fever, facial swelling, urticaria, hepatic injury, polyarthritis (idiosyncratic; Doberman over-represented)
• GI upset, anorexia
• Crystalluria / nephrotoxicity (poor hydration)
• Bone marrow suppression with prolonged use (folate antagonism) — supplement folate if >3 weeks
• Hypothyroidism with prolonged use (sulfa effect on thyroid)

Drug interactions

• Antacids (Mg, Al, Ca, Fe): reduce TMP-S absorption — separate by 2 h
• Cyclosporine: increased nephrotoxicity risk
• Methotrexate: additive folate antagonism — avoid
• Phenytoin: TMP-S can elevate phenytoin levels
• Warfarin: TMP-S may potentiate anticoagulation
• Local anaesthetics (procaine): block sulfa effect (PABA structural analogue)

Pregnancy and lactation

Avoid in late pregnancy and neonates — sulfa displaces bilirubin → kernicterus risk. Folate antagonism could affect fetal development. FDA Category C.

Monitoring

• Schirmer tear test — baseline, day 14, monthly during chronic therapy
• CBC every 3 weeks if therapy >3 weeks
• Thyroid (T4) every 3 months if therapy >3 weeks
• Liver enzymes (ALT, ALP) every 3 weeks
• Hydration / urine output — prevent crystalluria
• Hypersensitivity signs — fever, polyarthritis, facial swelling

Toxicity and overdose

Idiosyncratic hypersensitivity (Doberman over-represented): fever, polyarthritis, KCS, hepatic injury, polymyositis. KCS can be permanent — do Schirmer test on every chronic case at baseline, day 14, and monthly. Bone marrow suppression with high-dose / long-duration therapy.

Management: Stop drug. Folinic acid (leucovorin) 1 mg/kg PO q24h to bypass folate antagonism. Hydration to prevent crystalluria. Symptomatic for hypersensitivity (corticosteroids, antihistamines, hepatoprotection).

Clinical pearls

• Canine UTI: 15 mg/kg PO q12h × 14 days; cheap, effective for first-line empirical therapy
• Pneumocystis pneumonia in dog with chemotherapy / immunosuppression: 30 mg/kg PO q6h × 21 days saves lives — under-recognised diagnosis
• EPM in horses: TMP-S 30 mg/kg PO q12h + pyrimethamine 1 mg/kg PO q24h × 90–180 days; mandatory folate supplementation
• Doberman owner sensitivity: warn about idiosyncratic hypersensitivity (polyarthritis, hepatic injury) — alternative antibiotic preferred
• Dry-eye monitoring: Schirmer test mandatory for any chronic TMP-S course — KCS can be irreversible
• IV form for hospitalised cattle / horses gets rapid concentrations during severe sepsis

Mechanism of action

Synergistic sequential block of the bacterial folate pathway: sulfadiazine blocks dihydropteroate synthase (DHPS) → inhibits PABA → dihydropteroate conversion; trimethoprim blocks dihydrofolate reductase (DHFR) → inhibits dihydrofolate → tetrahydrofolate. Each agent alone is bacteriostatic; combination is bactericidal due to the cumulative inhibition. Mammals have intact preformed folate uptake → minimal direct toxicity in healthy hosts, but folate antagonism manifests in prolonged use.

Formulations and products

• Tribrissen tablet (combined): 80 mg TMP + 400 mg Sulfa
• Tribrissen tablet (combined): 5 mg TMP + 25 mg Sulfa
• Tribrissen oral suspension (combined) 48 mg/mL total
• TMP-Sulfa 24 % injection 240 mg/mL combined
• Tribrissen 400 oral paste — 67 mg TMP + 333 mg sulfadiazine per g (400 mg/g combined), 37.5 g syringe (Plumb’s p.1090; Papich 5e p.944)
• Sterbac SD Bolus (Micro Animal Health Care (Micro Labs group), Bengaluru) — Trimethoprim 200 mg + Sulphadiazine 1000 mg, Oral bolus
• Sterbac SD Powder (Micro Animal Health Care (Micro Labs group), Bengaluru) — Trimethoprim 2 % w/w + Sulphadiazine 10 % w/w, Oral powder

Storage

15–25 °C protected from light. Suspension: refrigerate; shake well.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other antibiotics

• Tildipirosin
• Tilmicosin
• Tinidazole
• Tobramycin
• Tulathromycin
• Tylvalosin
• Vancomycin

Frequently asked questions