Sulfadimidine is the same drug as sulfamethazine, the ingredient in Sulmet that used to be available in feed stores in the US until antibiotics were removed from shelves several years ago. It is a sulfonamide that can treat coccidiosis, coryza, and fowl cholera. Sulfadimethoxine is probably a better choice. Some also use Bactrim, Sulaftrim, or SMZ-TMP by prescription.