Is there a difference between sulfa and sulfite allergies?
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. Table 1 lists common medications that contain 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.
|Table 1. Sulfonamide drug classes/individual drugs that may cause allergic reactions|
Carbonic anhydrase inhibitor
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.
Some sulfiting agents are FDA approved preservatives that are added to food and pharmaceuticals. The more common sulfiting agents are sodium sulfite (Na2SO3), sodium bisulfite (NaHSO3), and sodium metabisulfite (Na2S2O3). Examples of foods containing sulfites are listed in Table 2. An extensive list of sulfite-containing pharmaceutical products is published annually within the Red Book.
|Table 2. Common sulfite-containing foods|
The following mechanisms of sulfite sensitivity have been proposed:
- cholinergic reflex response to inhaled sulfur dioxide
- IgE mediated delayed hypersensitivity
- sulfite oxidase deficiency
No antibody or specific complement activity has been identified in association with sulfite exposure. However, asthmatics seem to be more prone to develop bronchospasm when challenged with sulfur dioxide.
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Meekins CV, Sullivan TJ, Gruchalla RS. Immunochemical analysis of sulfonamide drug allergy: identification of sulfamethoxazole-substituted human serum proteins. J Allergy Clin Immunol 1994;94(6):1017-24.
Simon RA. Adverse reactions to food and drug additives. Differential diagnosis of allergic disease: masqueraders of allergy. Immunol Allergy Clin North Am 1996;16(1):137