One of the more common drug allergies is that to sulfa drugs. Sulfa drugs are more appropriately labeled sulfonamides and are derivatives of para-amino benzoic acid. The following list contains common medications that have a sulfonamide component. A sulfonamide allergy is different from a sulfite allergy because sulfonamides and sulfites are distinctly different chemicals. A person allergic to sulfites is no more likely to be allergic to sulfonamides than any other individual. Sulfonamide drug classes/individual drugs that may cause allergic reactions include:
Sulfonamide antibiotics, sulfadiazine, sulfamethoxazole, sulfasalazine, sulfisoxazole, sulfacetamide, sulfanilamide, sulfathiazole, sulfabenzamide, Thiazide diuretics, hydrochlorothiazide, chlorothiazide, metolazone, chlorthalidone, indapamide, methyclothiazide, Loop Diuretics, furosemide, Sulfonylureas, chlorpropamide, tolbutamide, tolazamide, glipizide, glyburide, Carbonic anhydrase inhibitor, and acetazolamide.

The mechanism of the sulfonamide drug allergy is immune mediated. When a sulfonamide is metabolized in the body, the drug is capable of attaching to human proteins, forming a larger molecule and possibly launching an immune response.

In contrast, sulfiting agents refer to a group of chemicals that include sulfur dioxide, sulfite salts, and sulfate salts. Sulfur dioxide is considered to be the offending component in a sulfite allergy. Sulfites and sulfates are metabolized to sulfur dioxide under certain conditions that depend on concentration, heat, and pH.