# Sulfadiazine: veterinary dose and monograph

> Sulfadiazine is a veterinary antibiotic. A short-acting sulfonamide antibacterial — most useful (and most used) POTENTIATED with trimethoprim (the "S" of trimethoprim-sulfadiazine / co-trimazine), which makes the combination bactericidal and broadens the spectrum. Indications include susceptible systemic, urinary, respiratory and enteric infections (with trimethoprim); toxoplasmosis / Neospora (sulfadiazine + pyrimethamine); coccidiosis (sulfonamide activity). This monograph lists 5 reference doses for dogs, cats, cattle and horses, each with route, frequency and source, plus meat and milk withdrawal periods for food animals.

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

## At a glance

- **Drug class:** Antibiotic
- **Also known as:** Sulphadiazine, Sulfadiazine sodium, Co-trimazine (with TMP)
- **Species with doses:** Dogs, Cats, Cattle and Horses
- **General dose range:** 15–30 mg/kg PO q12h (usually potentiated with trimethoprim) — check the species tables for the indication
- **Routes:** PO, IV
- **Last reviewed:** 1 October 2026

## Indications

- Susceptible systemic, urinary, respiratory and enteric infections (with trimethoprim)
- Toxoplasmosis / Neospora (sulfadiazine + pyrimethamine)
- Coccidiosis (sulfonamide activity)
- Nocardiosis and some other infections (adjunct)

## Sulfadiazine 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

*Sulfadiazine doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection (as TMP-sulfadiazine) | 15–30 mg/kg | PO | q12h (30 mg/kg may be q12–24h) | — |

- Susceptible infection (as TMP-sulfadiazine): Doses are the COMBINED trimethoprim + sulfonamide. Papich 5e: 15 mg/kg PO q12h or 30 mg/kg q12–24h; toxoplasmosis 30 mg/kg q12h. Plumb’s p.1089: UTI 30 mg/kg q24h or 15 mg/kg q12h; chronic pyoderma 30 mg/kg q12h for 21–42 days; bacteraemia 30–45 mg/kg q12h (Greene). Sulfadiazine alone (Papich): 100 mg/kg load then 50 mg/kg q12h. Ensure hydration; check Schirmer tear tests on longer courses; watch for hypersensitivity, hepatopathy and cytopenias (Dobermans).

### Cats

*Sulfadiazine doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Toxoplasmosis (with pyrimethamine) / susceptible infection | 15–30 mg/kg | PO | q12h | — |

- Toxoplasmosis (with pyrimethamine) / susceptible infection: COMBINED TMP + sulfonamide dose. Papich 5e: 15 mg/kg q12h or 30 mg/kg q12–24h; toxoplasmosis 30 mg/kg q12h. Plumb’s p.1089: toxoplasmosis 15 mg/kg PO q12h for 28 days (Lappin); UTI 30 mg/kg q24h or 15 mg/kg q12h for 7–14 days. Bitter — may cause salivation; monitor CBC.

### Cattle

*Sulfadiazine doses for cattle*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Susceptible infection (potentiated sulfonamide) | 16–48 mg/kg | IV | q24h | — | Withdrawal NOT established — treat as extra-label |

- Susceptible infection (potentiated sulfonamide): COMBINED dose. Papich 5e: no approved US doses; trimethoprim is not absorbed orally in ruminants (it is in calves); TMP-sulfadoxine 16 mg/kg IV or IM q24h has been used. Plumb’s p.1089: 25 mg/kg IV or IM q24h (Burrows); 44 mg/kg IM or IV of the 48% suspension (Upson); calves 48 mg/kg (Baggot). Extra-label — obtain a FARAD withdrawal.

### Horses

*Sulfadiazine doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Susceptible infection (potentiated sulfonamide) | 15–30 mg/kg | PO | q12h | — |
| EPM (sulfadiazine with pyrimethamine) | 20 mg/kg | PO | q24h, 1 h before hay or grain | 90–270 days |

- Susceptible infection (potentiated sulfonamide): COMBINED dose. Papich 5e: label oral suspension 24 mg/kg (20 sulfadiazine + 4 TMP) q12h for 10 days; many use 25–30 mg/kg q12h. Plumb’s p.1089: 15–30 mg/kg PO q12h, 30 min before hay (Foreman); foals 15 mg/kg IV q12h or 30 mg/kg PO q12h. Do NOT give IV potentiated sulfonamides with detomidine or other alpha-2 agonists (fatal arrhythmias).
- EPM (sulfadiazine with pyrimethamine): Plumb’s p.1033 (ReBalance label): sulfadiazine 20 mg/kg with pyrimethamine 1 mg/kg (4 mL per 50 kg) PO once daily; duration by clinical response. Monitor CBC (folate-related cytopenias).

### Buffalo

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

*Sulfadiazine doses for buffalo*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Susceptible infection (potentiated sulfonamide) | 16–48 mg/kg | IV | q24h | — | Withdrawal NOT established — treat as extra-label |

- Susceptible infection (potentiated sulfonamide): COMBINED dose. Papich 5e: no approved US doses; trimethoprim is not absorbed orally in ruminants (it is in calves); TMP-sulfadoxine 16 mg/kg IV or IM q24h has been used. Plumb’s p.1089: 25 mg/kg IV or IM q24h (Burrows); 44 mg/kg IM or IV of the 48% suspension (Upson); calves 48 mg/kg (Baggot). Extra-label — obtain a FARAD withdrawal.

## Contraindications

Sulfonamide hypersensitivity (Dobermanns are predisposed to idiosyncratic reactions). Pre-existing KCS, significant hepatic/renal disease, or blood dyscrasias. Dehydration/aciduria (crystalluria risk — ensure hydration). Pregnancy near term (kernicterus concern). Known hypersensitivity.

## Species-specific warnings

> **Caution:** Dogs: Dobermanns (and other large breeds) are predisposed to idiosyncratic sulfonamide hypersensitivity (fever, polyarthritis, hepatopathy, blood dyscrasias) — monitor and discontinue promptly if suspected.

## Adverse effects

- Keratoconjunctivitis sicca (KCS) — sulfonamide class, monitor tear production
- Idiosyncratic hypersensitivity (fever, polyarthritis, skin/hepatic reactions) — esp. Dobermanns
- Blood dyscrasias (anaemia, thrombocytopenia, neutropenia)
- Crystalluria/urolithiasis in acidic/concentrated urine; hepatotoxicity

## Drug interactions

- Trimethoprim: synergistic (the potentiated combination)
- IV potentiated sulfonamides + alpha-2 agonists (detomidine/romifidine) in HORSES: fatal arrhythmias reported — avoid
- Warfarin/methotrexate: potentiated (protein-binding/folate effects)
- Antacids/urinary alkalinisers: alter absorption/crystalluria; PABA-containing products antagonise

## Pregnancy and lactation

Avoid near term (kernicterus/folate concerns); folate supplementation reduces cytopenia risk with prolonged use.

## Monitoring

- Schirmer tear test (KCS) on courses beyond ~1–2 weeks
- CBC (blood dyscrasias) and liver values on prolonged therapy
- Hydration/urine (crystalluria); idiosyncratic-reaction signs (fever, joint pain) — especially Dobermanns
- Clinical response; folate status in protracted use

## Toxicity and overdose

Sulfonamide-class toxicities dominate: KCS (dose/duration-related, sometimes permanent — monitor Schirmer test), idiosyncratic hypersensitivity (Type III — fever, polyarthropathy, hepatopathy, skin, blood dyscrasias, especially in Dobermanns), crystalluria/uroliths in acidic urine, and folate-deficiency cytopenias with prolonged use. Acute overdose otherwise has a fairly wide margin.

Management: No specific antidote. Discontinue; ensure hydration and alkalinise urine to clear crystalluria; supportive care. For idiosyncratic reactions, stop the drug and treat immune-mediated signs (± corticosteroids). Folinic acid (leucovorin) supports marrow with folate-related cytopenias. Monitor tear production, CBC and liver values.

## Clinical pearls

- Almost always used POTENTIATED with trimethoprim — the pair is synergistic/bactericidal, whereas sulfadiazine alone is bacteriostatic
- A cornerstone (with pyrimethamine) of toxoplasmosis/Neospora therapy, with good tissue/CSF penetration
- Watch the classic sulfonamide toxicities: KCS (Schirmer-test monitor), idiosyncratic reactions (Dobermanns), crystalluria (keep hydrated) and cytopenias (folate)
- In horses, never give IV potentiated sulfonamides alongside alpha-2 sedatives (fatal arrhythmias reported)

## Mechanism of action

A sulfonamide that competitively inhibits dihydropteroate synthase, blocking bacterial/protozoal incorporation of para-aminobenzoic acid (PABA) into folate — halting folate (and thus nucleic-acid) synthesis. Alone it is bacteriostatic; combined with trimethoprim (which inhibits the next step, dihydrofolate reductase) it produces sequential folate-pathway blockade that is synergistic and bactericidal. Mammalian cells use preformed folate, giving selectivity.

## Formulations and products

- 500 mg tablet (with/without trimethoprim)
- Injectable (with trimethoprim, potentiated sulfonamide)
- Sterbac SD Bolus (Micro Animal Health Care (Micro Labs group), Bengaluru) — Sulphadiazine 1000 mg + Trimethoprim 200 mg, Oral bolus
- Sterbac SD Powder (Micro Animal Health Care (Micro Labs group), Bengaluru) — Sulphadiazine 10 % w/w + Trimethoprim 2 % w/w, Oral powder
- Sulfadiazine (± trimethoprim) — 500 mg tablet, Tablet / injection (human-label)

## Storage

Tablets/injection: 15–30 °C, dry, protect from light.

## 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.

## Other antibiotics

- [Rifaximin](https://vetmasterji.com/drugs/rifaximin)
- [Silver Sulfadiazine](https://vetmasterji.com/drugs/silver-sulfadiazine)
- [Spectinomycin](https://vetmasterji.com/drugs/spectinomycin)
- [Streptomycin (Dihydrostreptomycin)](https://vetmasterji.com/drugs/streptomycin)
- [Sulfadimethoxine](https://vetmasterji.com/drugs/sulfadimethoxine)
- [Sulphadimidine (Sulfamethazine)](https://vetmasterji.com/drugs/sulphadimidine)
- [Tiamulin](https://vetmasterji.com/drugs/tiamulin)
- [Tildipirosin](https://vetmasterji.com/drugs/tildipirosin)

## Frequently asked questions

### What is the dose of Sulfadiazine for dogs?

Reference doses for Sulfadiazine in dogs: 15–30 mg/kg PO q12h (30 mg/kg may be q12–24h) (Susceptible infection (as TMP-sulfadiazine)). Confirm against the label and the patient before use.

### What is the dose of Sulfadiazine for cats?

Reference doses for Sulfadiazine in cats: 15–30 mg/kg PO q12h (Toxoplasmosis (with pyrimethamine) / susceptible infection). Confirm against the label and the patient before use.

### What is the dose of Sulfadiazine for cattle?

Reference doses for Sulfadiazine in cattle: 16–48 mg/kg IV q24h (Susceptible infection (potentiated sulfonamide)). Confirm against the label and the patient before use.

### What is the withdrawal period for Sulfadiazine?

Cattle, IV (Susceptible infection (potentiated sulfonamide)): Withdrawal NOT established — treat as extra-label. Follow the product label and national regulations where they differ.

### When should Sulfadiazine not be used?

Sulfonamide hypersensitivity (Dobermanns are predisposed to idiosyncratic reactions). Pre-existing KCS, significant hepatic/renal disease, or blood dyscrasias. Dehydration/aciduria (crystalluria risk — ensure hydration). Pregnancy near term (kernicterus concern). Known hypersensitivity.

### What are the side effects of Sulfadiazine in animals?

Keratoconjunctivitis sicca (KCS) — sulfonamide class, monitor tear production; Idiosyncratic hypersensitivity (fever, polyarthritis, skin/hepatic reactions) — esp. Dobermanns; Blood dyscrasias (anaemia, thrombocytopenia, neutropenia); Crystalluria/urolithiasis in acidic/concentrated urine; hepatotoxicity.

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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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.