Sulfamethazine

Sulfamethazine, also called sulfadimidine, is a sulfonamide antimicrobial used principally in livestock and poultry. Applications include selected susceptible bacterial infections and intestinal coccidiosis. Veterinary products differ in concentration, route and release characteristics, and the clinical spectrum depends on the organism and the species-specific formulation.

Group

Sulfonamide antibacterial

Mechanism of Action

Sulfamethazine competes with para-aminobenzoic acid for microbial dihydropteroate synthase. Reduced folate synthesis limits production of nucleic-acid precursors and inhibits growth of susceptible bacteria and coccidia. The effect is principally bacteriostatic or coccidiostatic. Susceptibility and exposure determine whether this interruption of folate metabolism produces a useful clinical response.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Susceptible infection — Loading	100 mg/kg	PO	Once
Susceptible infection — Maintenance	50 mg/kg	PO	Every 12 h	Reported notes uncommon use in small animals.

Cats

Use / stage	Dose	Route	Schedule	Instructions
Susceptible infection — Loading	100 mg/kg	PO	Once
Susceptible infection — Maintenance	50 mg/kg	PO	Every 12 h	Reported notes uncommon use in small animals.

Cattle

Use / stage	Dose	Route	Schedule	Instructions
Parenteral antibacterial treatment — Maintenance	110 mg/kg	IV	Every 24 h
Oral antibacterial treatment — Loading	237 mg/kg	PO	Once	Drench or drinking-water regimen.
Oral antibacterial treatment — Maintenance	119 mg/kg	PO	Every 24 h
Sustained-release antibacterial treatment	350–400 mg/kg	PO	Once
Calf antibacterial treatment	180 mg/kg	PO	Every 24 h	Calves only.

Pigs

Use / stage	Dose	Route	Schedule	Instructions
Oral antibacterial treatment — Loading	237 mg/kg	PO	Once	Drench or drinking-water regimen.
Oral antibacterial treatment — Maintenance	119 mg/kg	PO	Every 24 h

Horses

Use / stage	Dose	Route	Schedule	Instructions
Oral antibacterial treatment — Initial	222 mg/kg	PO	Every 24 h	Up to 1 days
Oral antibacterial treatment — Maintenance	111 mg/kg	PO	Every 24 h

Indications

Treatment of selected susceptible bacterial respiratory, enteric or soft-tissue infections in livestock with an indicated product.
Treatment of selected bovine calf diphtheria, foot rot or other susceptible bacterial disease where covered by the product indication.
Treatment or control of coccidiosis in cattle, poultry or other supported veterinary species.

Contraindications

Sulfonamide hypersensitivity
Doberman pinschers may have greater susceptibility to reactions.

Interactions

Warfarin, methenamine, dapsone, etodolac, methotrexate and pyrimethamine may interact; cyclosporine exposure may fall.
IV trimethoprim-sulfonamide combinations with equine detomidine can provoke arrhythmias; this warning is not a general oral interaction.

Adverse effects

Hypersensitivity, cytopenias, hepatopathy, keratoconjunctivitis sicca, arthropathy and thyroid suppression with prolonged therapy.

Preparations

Preparation	Form	Strength	Route
Sulfamethazine bolus 30 g	Tablet	30 g / tablet	PO
Sulfamethazine injection 250 mg/mL	Injection	250 mg / mL	IV

Monitoring and Administration

Assess clinical and microbiological response; monitor CBC, hepatic signs, tear production and thyroid interpretation during prolonged treatment. A combination dose must not be treated as a single sulfonamide component dose.

Cattle: Reported gives 220 mg/kg initial then 110 mg/kg every 24 hours IV, but does not explicitly attach a route to the loading amount.