Sulfonamides are medicines that prevent the growth of bacteria in the body. They are used to treat many kinds of infections caused by bacteria and certain other microorganisms. Doctors may prescribe these drugs to treat urinary tract infections, ear infections, frequent or long-lasting bronchitis, bacterial meningitis, certain eye infections, Pneumocystis carinii pneumonia, traveler's diarrhea, and a number of other kinds of infections. These drugs will not work for colds, flu, and other infections caused by viruses.

Sulfonamides (also called sulfa drugs) are available only by prescription in tablet and liquid forms. Some commonly-used sulfonamides are sulfisoxazole (Gantrisin) and the combination drug sulfamethoxazole and trimethoprim (Bactrim, Cotrim).

The recommended dosage depends on the type of sulfonamide, the strength of the medicine, and the medical problem for which it's being taken. Sulfonamides should always be taken exactly as directed and for the full course of medication to make sure the...