Drug, sulfa: One of the sulfonamides, the sulfa-related antibiotics which are used to treat bacterial and some fungal infections.

The first sulfa drug was prontosil. It was discovered by the German physician and chemist Gerhard Domagk in 1935. The sulfa family of drugs includes sulfadiazine, sulfamethizole (brand name: Thiosulfil Forte), sulfamethoxazole (Gantanol), sulfasalazine (Azulfidine), sulfisoxazole (Gantrisin), and various high-strength combinations of three sulfonamides.

Sulfa drugs kill bacteria and fungi by interfering with their metabolism. They were the "wonder drugs" before penicillin and are still used today. Because sulfa drugs concentrate in the urine before being excreted, treating urinary tract infections is one of their most common uses. Sulfa drugs can have a number of interactions with prescription and over-the-counter drugs (including PABA sunscreens), and are not appropriate for people with some health conditions.