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

> Trimethoprim / Sulfadiazine (TMP-Sulfa) is a veterinary antibiotic. Synergistic combination — trimethoprim blocks bacterial dihydrofolate reductase, sulfa blocks dihydropteroate synthase; sequential block on the same folate pathway → bactericidal at clinical concentrations. Indications include UTI (susceptible E. coli, Proteus, Staphylococcus); pyoderma / skin & soft tissue infection; respiratory infection (CIRDC, BRD). This monograph lists 17 reference doses for dogs, cats, cattle, horses, pigs and birds and 7 more species, each with route, frequency and source, plus meat and milk withdrawal periods for food animals.

Source: https://vetmasterji.com/drugs/tmp-sulfa · Last reviewed: 2026-10-01

## 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

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| UTI / pyoderma / soft tissue | 15–30 mg/kg | PO | q12h | 7–14 days |
| Pneumocystis carinii pneumonia | 30 mg/kg | PO | q12h (or 15 mg/kg q8h) | 21 days |
| Toxoplasmosis / Neospora | 15–30 mg/kg | PO | q12h | 4 weeks |

- 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

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection | 15–30 mg/kg | PO | q12h | — |

- 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

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for cattle*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Susceptible infection (extra-label) | 25 mg/kg | IV | q24h | — | Withdrawal NOT established — treat as extra-label |
| Calves — susceptible infection (extra-label) | 48 mg/kg | IV | q24h | — | Withdrawal NOT established — treat as extra-label |

- 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

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection | 24–30 mg/kg | PO | q12h | — |
| EPM (Sarcocystis neurona) | 24–30 mg/kg | PO | q12h | 90–120 days (or longer) |

- 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

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for pigs*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Susceptible infection | 48 mg/kg | IM | q24h | — | Withdrawal NOT established — treat as extra-label |

- 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.

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for buffalo*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Susceptible infection (extra-label) | 25 mg/kg | IV | q24h | — | Withdrawal NOT established — treat as extra-label |
| Calves — susceptible infection (extra-label) | 48 mg/kg | IV | q24h | — | Withdrawal NOT established — treat as extra-label |

- 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

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for birds*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Psittacines — susceptible infection | 50–100 mg/kg | PO | q12h | — |

- 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

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for rabbits*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection (oral) | 15–30 mg/kg | PO | q12–24h | — |

- 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

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for ferrets*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection | 30 mg/kg | PO | q12h | — |

- 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

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for guinea pigs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection | 15–30 mg/kg | PO | q12h | — |

- 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

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for reptiles*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection | 30 mg/kg | IM | q24h × 2, then q48h | 5–12 further doses |

- 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

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for chinchillas*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection | 15–30 mg/kg | PO | q12h | — |

- 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

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for rats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection | 15–30 mg/kg | PO | q12h | — |

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

### Primates

*Trimethoprim / Sulfadiazine (TMP-Sulfa) doses for primates*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection (prosimians) | 30 mg/kg | PO | q24h | — |

- 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

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

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

> **Caution:** 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

> **Caution:** 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.

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## Frequently asked questions

### What is the dose of Trimethoprim / Sulfadiazine (TMP-Sulfa) for dogs?

Reference doses for Trimethoprim / Sulfadiazine (TMP-Sulfa) in dogs: 15–30 mg/kg PO q12h for 7–14 days (UTI / pyoderma / soft tissue); 30 mg/kg PO q12h (or 15 mg/kg q8h) for 21 days (Pneumocystis carinii pneumonia); 15–30 mg/kg PO q12h for 4 weeks (Toxoplasmosis / Neospora). Confirm against the label and the patient before use.

### What is the dose of Trimethoprim / Sulfadiazine (TMP-Sulfa) for cats?

Reference doses for Trimethoprim / Sulfadiazine (TMP-Sulfa) in cats: 15–30 mg/kg PO q12h (Susceptible infection). Confirm against the label and the patient before use.

### What is the dose of Trimethoprim / Sulfadiazine (TMP-Sulfa) for cattle?

Reference doses for Trimethoprim / Sulfadiazine (TMP-Sulfa) in cattle: 25 mg/kg IV q24h (Susceptible infection (extra-label)); 48 mg/kg IV q24h (Calves — susceptible infection (extra-label)). Confirm against the label and the patient before use.

### What is the withdrawal period for Trimethoprim / Sulfadiazine (TMP-Sulfa)?

Cattle, IV (Susceptible infection (extra-label)): Withdrawal NOT established — treat as extra-label; Cattle, IV (Calves — susceptible infection (extra-label)): Withdrawal NOT established — treat as extra-label; Pigs, IM (Susceptible infection): Withdrawal NOT established — treat as extra-label. Follow the product label and national regulations where they differ.

### When should Trimethoprim / Sulfadiazine (TMP-Sulfa) not be used?

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).

### What are the side effects of Trimethoprim / Sulfadiazine (TMP-Sulfa) in animals?

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).

## Sources

- Plumb's Veterinary Drug Handbook
- Papich, Papich Handbook of Veterinary Drugs, 5th edition
- Carpenter, Exotic Animal Formulary

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.