Sulfamethazine

Sulfamethazine is a sulfonamide antibiotic used primarily in veterinary medicine. As a synthetic antimicrobial, it inhibits dihydropteroate synthase in bacterial folate synthesis, producing a bacteriostatic effect. It is widely used to treat infections in livestock such as cattle, pigs, and poultry and is often combined with trimethoprim to provide synergistic activity and broaden the spectrum of action.

Pharmacokinetics: sulfamethazine is usually administered orally, is absorbed from the gastrointestinal tract, and distributes widely in body tissues. It is excreted largely by the kidneys, with a species-dependent elimination half-life. Adequate hydration is important because sulfonamides can precipitate in the urine, potentially causing crystalluria or nephrotoxicity in susceptible animals.

Adverse effects and safety: potential adverse reactions include hypersensitivity, gastrointestinal upset, and, particularly in dehydrated animals or when used with other folate antagonists, nephrotoxicity or hematologic changes. In humans, exposure to veterinary drug residues may rarely provoke allergic reactions. Caution is advised in breeding females and young animals.

Resistance and regulation: resistance to sulfonamides is common and can involve altered target enzymes or reduced drug uptake, with possible cross-resistance to related sulfonamides. Because drug residues can persist in meat or milk, withdrawal times apply in many countries, and non-therapeutic uses such as growth promotion have been restricted or prohibited in many jurisdictions.