Sulfa drugs are a broad group of pharmaceuticals based on sulfonamide. The earliest group of these drugs were used for their anti-bacterial properties, but now include anti-convulsants and diuretics. These drugs must be used with caution because they often cause allergic reactions.
Sulfa drugs were developed in the 1930s when a team of German chemists working for Bayer noted that one of the dyes they were testing for medical applications killed some types of bacteria, but only in a living subject and never in a test tube. Working from this result, a French team realized that the dye was breaking down in the body and that sulfonamide was the active ingredient. Sulfonamide was an off-patent chemical (also used as a dye) and could be produced without paying royalties. Drugs bases on sulfonamide quickly came into widespread use.
However, early formulations of sulfonamide often had disastrous results and, in the United States, led to the strengthening of the Food and Drug Administration.
Although sulfa drugs were an important breakthrough at the time, they were eventually replaced in most anti-bacterial applications by antibiotics. In addition to allergies, about 3% of patients suffered other adverse effects, such as crystallization of the drug in the kidneys due to its low solubility in water, to serious diseases such as Stevens-Johnson syndrome and toxic epidermal necrolysis. Patients with AIDS are over 60% likely to develop complications. Sulfa drugs can also cause attacks in porphyria patients.
However, sulfa drugs are coming back into use to treat antibiotic resistant bacteria.