Sulfa drug

Overview
The term sulfa drug refers to the class of medications called sulfonamides. This class includes several antibiotics, including sulfamethoxazole, sulfasalazine, and sulfacetamide, among others.

It is important to make a distinction between sulfa drugs and other sulfur-containing drugs and additives, such as sulfates and sulfites, which are chemically unrelated to the sulfonamide group, and do not cause the same hypersensitivity reactions seen in the sulfonamides.

Functions
These antibiotics are used to treat pneumocystis jiroveci pneumonia, urinary tract infections, shigellosis, and certain protozoan infections.

The sulfonamide chemical moiety is also present in other medications that are not antimicrobials, including thiazide diuretics (including hydrochorothiazide, metolazone, and indapamide, among others), sulfonylureas (including glipizide, glyburide, among others), and acetazolamide.

Sulfasalazine, in addition to its use as an antibiotic, is also utilized in the treatment of inflammatory bowel disease.

Adverse reactions
Approximately 3% of the general population have adverse reactions when treated with sulfonamide antimicrobials. Of note is the observation that patients with HIV have a much higher prevalence, at about 60%. People who have a hypersensitivity reaction to one member of the sulfonamide class are likely to have a similar reaction to others.

Hypersensitivity reactions are less common in non-antibiotic sulfonamides, and, though controversial, the available evidence suggests those with hypersensitivity to sulfonamide antibiotics do not have an increased risk of hypersensitivity reaction to the non-antibiotic agents.

Two regions of the sulfonamide antibiotic chemical structure are implicated in the hypersensitivity reactions associated with the class.
 * The first is the N1 heterocyclic ring, which causes a type I hypersensitivity reaction.
 * The second is the N4 amino nitrogen that, in a stereospecific process, forms reactive metabolites that cause either direct cytotoxicity or immunologic response.

The non-antibiotic sulfonamides lack both of these structures.

The most common manifestation of a hypersensitivity reaction to sulfa drugs are rash and hives. However, there are several life-threatening manifestations of hypersensitivity to sulfa drugs, including Stevens-Johnson syndrome, toxic epidermal necrolysis, agranulocytosis, hemolytic anemia, thrombocytopenia, and fulminant hepatic necrosis, among others.