Sulfadimidine is an alternative term for sulfamethazine, the widely used sulfonamide drug for livestock. The dual naming reflects the British (sulphadimidine) and international spellings of the same compound, a source of potential confusion in residue records and veterinary prescriptions. Like other sulfonamides it is used to control bacterial and protozoal infections in swine and cattle and has been used as a growth promoter. Rapid absorption and excretion characterize its pharmacokinetics, and withdrawal periods protect the food chain from residues. Veterinarians must respect the same withdrawal periods regardless of which spelling appears on the product label.