Sulfonamides are a group of pharmaceuticals based on the functional chemical group by the same name. They include the sulfa drugs.
Patients who are allergic to one of the sulfonamide drugs are likely to be allergic to the entire class. Allergic reactions are common. They can also lead to hyperbilirubinemia that can lead to brain damage. Patients with HIV are particularly susceptible to these side effects.
Most sulfonamide pharmaceuticals are used as antibiotics, but some are used as diuretics, anticonvulsants, and COX-2 inhibitors.