Sulphadimidine (Sulfamethazine): veterinary dose and monograph

At a glance

Drug class

Antibiotic

Also known as

Sulfamethazine, Sulfadimidine, Sulmet, Sulfaster-Vet

Species with doses

Dogs, Cattle, Horses and Pigs

General dose range

110–237 mg/kg PO loading dose (≈220–237 mg/kg) then half dose q24h — check the species tables for the indication

Routes

PO, IV

Last reviewed

1 October 2026

Indications

• Bloody diarrhoea and dysentery
• Pneumonia / respiratory infection
• Foot rot
• Coccidiosis
• Susceptible enteric and urinary infections

Sulphadimidine (Sulfamethazine) 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 (rarely used): Papich 5e (dogs and cats): 100 mg/kg PO loading dose followed by 50 mg/kg q12h. Watch for KCS, hypersensitivity and crystalluria.

Cattle

• Pneumonia / enteric infection (oral drench or water): Papich 5e (sulfamethazine): soluble powder as drench or in water 237 mg/kg initially, then 119 mg/kg q24h PO; calves 180 mg/kg PO per day; sustained-release bolus 350–400 mg/kg PO once. Not in Plumb’s. Keep well hydrated (crystalluria). Withdrawal depends on formulation — follow the local label; many labels exclude lactating dairy cattle.
• Pneumonia / systemic infection (IV): Papich 5e: 220 mg/kg as the initial dose followed by 110 mg/kg q24h IV. Follow the local label or FARAD withdrawal.

Horses

• Susceptible infection: Papich 5e: 222 mg/kg PO per day on day 1 and 111 mg/kg PO per day thereafter.

Goats

• No reference dose for this species: Papich 5e gives no goat dose for sulfamethazine and Plumb’s has no monograph. The previous row was scaled from a product catalogue.

Sheep

• No reference dose for this species: Papich 5e gives sulfamethazine doses for cattle, pigs, horses, dogs and cats but not sheep, and Plumb’s has no monograph. The previous row was scaled from a product catalogue.

Pigs

• Enteric infection: Papich 5e: soluble powder as a drench or in drinking water 237 mg/kg initially, then 119 mg/kg q24h PO. Follow the local label withdrawal.

Buffalo

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

• Pneumonia / enteric infection (oral drench or water): Papich 5e (sulfamethazine): soluble powder as drench or in water 237 mg/kg initially, then 119 mg/kg q24h PO; calves 180 mg/kg PO per day; sustained-release bolus 350–400 mg/kg PO once. Not in Plumb’s. Keep well hydrated (crystalluria). Withdrawal depends on formulation — follow the local label; many labels exclude lactating dairy cattle.
• Pneumonia / systemic infection (IV): Papich 5e: 220 mg/kg as the initial dose followed by 110 mg/kg q24h IV. Follow the local label or FARAD withdrawal.

Contraindications

Known sulfonamide hypersensitivity. Severe hepatic or renal impairment. Dehydration — maintain water intake, since crystalluria and tubular obstruction follow concentrated urine. Avoid rapid IV administration of injectable sulfonamides (see toxicity). Sulfonamides depress ruminal cellulolytic microflora; the effect is usually transient but matters in an already-inappetent ruminant. Not for use where a withdrawal period cannot be observed — sulfonamides diffuse passively into milk and residues are readily detected.

Species-specific warnings

Cattle: No withdrawal period is established in the uploaded references and Indian catalogues state none. Sulfonamides diffuse into milk and residues are readily detected — do not return milk to the tank without checking your national label.

Goats: Goats clear many drugs faster than sheep; monitor clinical response. No withdrawal figure available.

Adverse effects

• Crystalluria with haematuria, and rarely tubular obstruction (uncommon in veterinary patients)
• Acute toxicity after too-rapid IV or excessive dose: muscle weakness, ataxia, BLINDNESS, collapse
• GI disturbance — nausea, vomiting, disturbed microfloral balance and reduced vitamin B synthesis
• Transient depression of ruminal cellulolytic function
• Prolonged treatment: bone marrow depression (aplastic anaemia, granulocytopenia, thrombocytopenia)
• Hepatitis and icterus
• Peripheral neuritis and myelin degeneration of spinal cord and peripheral nerves
• Photosensitisation, stomatitis, conjunctivitis, keratoconjunctivitis sicca
• Mild follicular thyroid hyperplasia

Drug interactions

• Trimethoprim / ormetoprim: SYNERGISTIC — sequential blockade of the folate pathway converts a bacteriostatic sulfonamide into a bactericidal combination (this is the basis of the potentiated sulfonamides)
• Procaine and other PABA-releasing local anaesthetics: antagonise sulfonamide action — avoid concurrently
• Pus and necrotic tissue: high local PABA antagonises activity — debride before relying on a sulfonamide
• Other bone-marrow suppressants: additive haematological toxicity on prolonged courses
• Urinary acidifiers: increase the risk of crystalluria

Pregnancy and lactation

Sulfonamides cross the placenta. No specific sulphadimidine reproductive-safety statement appears in the uploaded references — use only where the benefit justifies it, and prefer a better-characterised agent in late gestation.

Monitoring

• Hydration and urine output — crystalluria risk rises in concentrated urine
• Appetite and rumen function in ruminants
• CBC on courses beyond a few days (marrow suppression)
• Liver enzymes / icterus on prolonged treatment
• Eyes — tear production (KCS) and conjunctivitis on prolonged courses
• Withdrawal compliance: no figure is established here, so confirm against the national label before milk or meat enters the chain

Toxicity and overdose

Merck: acute toxic manifestations follow too-rapid IV administration or an excessive dose, and present as muscle weakness, ataxia, BLINDNESS and collapse. Crystalluria with haematuria and tubular obstruction is described but uncommon in veterinary patients; maintaining hydration and urine flow is the main preventive. Prolonged courses carry the serious risks: bone marrow depression (aplastic anaemia, granulocytopenia, thrombocytopenia), hepatitis with icterus, and peripheral neuritis with myelin degeneration. Keep courses short and ensure free access to water.

Clinical pearls

• Give the LOADING dose — halving it from the start is the commonest reason sulphadimidine appears to fail
• Ensure free access to water throughout; the classical toxicity is crystalluria in a dehydrated animal
• Debride pus before relying on it — PABA in necrotic tissue directly antagonises sulfonamides
• Pairing with trimethoprim (as in the potentiated sulfonamides) is bactericidal and allows much lower doses
• Blindness is a recognised sign of acute sulfonamide overdose — worth knowing before it is mistaken for something else

Mechanism of action

Sulfonamide. Competitively inhibits dihydropteroate synthase, blocking incorporation of para-aminobenzoic acid (PABA) into dihydrofolic acid and so halting bacterial folate synthesis — bacteriostatic. Mammalian cells take up preformed folate and are unaffected, which is the basis of selectivity. Because the block is competitive with PABA, activity falls in necrotic tissue and pus (high local PABA). Merck notes sulfamethazine distributes widely — concentrations in skin, liver and lung approach plasma levels, muscle and bone reach about half, CSF 20–80%, and passive diffusion into milk occurs at concentrations usually too low to treat infection but high enough to be detected as residue.

Formulations and products

• Sulfaster-Vet 5 g sulphadimidine tablet/bolus (Micro Animal Health Care)
• Sulfaster-Vet (Micro Animal Health Care (Micro Labs group), Bengaluru) — Sulphadimidine 5 g, Oral tablet / bolus

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

• Spectinomycin
• Streptomycin (Dihydrostreptomycin)
• Sulfadiazine
• Sulfadimethoxine
• Tiamulin
• Tildipirosin
• Tilmicosin
• Tinidazole

Frequently asked questions