Sulfa drug allergy

Sulfa, sulphite, sulphate and sulfur – they sound very similar but are absolutely not, and a sensitivity to one certainly does not mean sensitivity to all. For more information in the food preservative (and allergen) sulphite and the very necessary chemical elements sulphur and sulphates, see section on sulphites.

'Sulfa' refers to sulfonamides, a group of drugs that includes those with and without antibiotic characteristics. Antibiotic sulfonamides were the first antibiotics used to treat infections, although, because of their common side effects, they are much less used today. The antibiotic sulfonamides are structurally different from the non-antibiotic sulfonamides, and appear to be much more likely to result in allergic reactions.


Skin reactions are the most common reactions to sulfa medications and can run from benign rashes to life-threatening Stevens-Johnson syndrome and toxic epidermal necrolysis. Hives and increased sensitivity to sunlight (photosensitivity) are also possible. If the sulfa medication is continued the reactions may become more serious.

Liver and kidney injury. People with sulfa allergy may also develop a type of hepatitis, and kidney failure, as a result of sulfa medications.

Lung reactions. Sulfa allergy can also affect the lung, with pneumonia-like reactions, worsening asthma and vasculitis occurring.

Blood reactions. Sulfa allergy can also affect various blood cells, resulting in decreased white blood cells, red blood cells, and platelets, through an immunologic-mediated manner.

For more on sulfa allergy including a list of drugs which contain sulfa, see

First published in March 2010

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