Sulfa drugs (sulfonamides) were the first chemical substances used to cure and prevent bacterial infections in humans. Although the active ingredient, sulfanilamide, was first synthesized in 1908, it wasn't until 1932 that scientists discovered that it could cure streptococcal infections in mice. Sulfonamides are bacteriostatic drugs. They do not kill bacteria but inhibit growth and multiplication by interfering with their enzyme systems. Coupled with the body's defense mechanism, sulfa drugs can be used to control infection.
All the sulfonamides are somewhat toxic, producing blood abnormalities and kidney damage when improperly used. Although more than 5,000 variations have been prepared and tested, fewer than 20 continue to have therapeutic value because resistant strains of bacteria have developed. Eventually, sulfa drugs were largely displaced by the discovery of antibiotics, which are far less toxic. New safer sulfonamides are still often used for treating urinary tract infections and vaginal yeast infections, and are sometimes used to treat infections that are antibiotic resistant.