Sulfadiazine: veterinary dose and monograph

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

• 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

• 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

• 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

• 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.

• 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

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

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
• Silver Sulfadiazine
• Spectinomycin
• Streptomycin (Dihydrostreptomycin)
• Sulfadimethoxine
• Sulphadimidine (Sulfamethazine)
• Tiamulin
• Tildipirosin

Frequently asked questions