Sulfonamides are a group of synthetic organic antibacterials with broad-spectrum activity. They are widely used to fight bacterial and protozoal infections in animals, especially digestive- and respiratory-tract diseases, administered by every known route, often at doses well above human ones. Residues clear from liver, kidney, and milk earlier than from muscle and adipose tissue, so withdrawal periods are set accordingly. Examples include sulfamethazine, sulfanilamide, and sulfathiazole. Resistance management and residue monitoring remain central to their responsible use. They remain among the most widely used veterinary antimicrobials worldwide.