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Sulfonamide antibiotic allergy

pdfASCIA PCC Sulfonamide antibiotic allergy 2015143.47 KB

Note: This document uses spelling according to the Australian Therapeutic Goods Administration (TGA) approved terminology for medicines (1999) in which the terms sulfur, sulfite, sulfate, and sulfonamide replace sulphur, sulphite, sulphate and sulphonamide.

Being told that one is allergic to sulfur commonly causes confusion, as many people wrongly assume that they will be allergic to multiple sulfur containing medicines or sulfite preservatives.  It is important to know that sulfur is an important building block of life, and that allergic reactions to sulfonamide (sometimes called sulfur) antibiotics do not increase the likelihood that a person will also be allergic to sulfur powder, sulfite preservatives, or non-antibiotic sulfonamide medicines like some pain killers or diuretics (water tablets).

Sulfonamide antibiotic allergy

Sulfonamide antibiotics can cause allergic reactions, ranging from mild to severe rashes through to anaphylaxis, the most severe type of allergic reaction. If you are allergic to one sulfonamide antibiotic, you should avoid all other sulfonamide antibiotics. Sulfonamide antibiotics available on prescription in Australia include:

  • Sulfamethoxazole used in combination with trimethoprim, available as Bactrim, Resprim or Septrin.
  • Less commonly used sulfonamide antibiotics include Sulfadiazine (tablets, injection or cream), Sulfadoxine (for malaria), and Sulfacetamide antibiotic eye drops.
  • Sulfasalazine (Salazopyrin, Pyralin), used in inflammatory bowel disease or arthritis, is a combination sulfapyridine (a sulfonamide antibiotic) and a salicylate.

If you have had an allergic reaction to Bactrim, Resprim or Septrin, there is no way of knowing whether the allergy was to sulfamethoxazole or to trimethoprim, therefore you should avoid trimethoprim (Alprim, Triprim) as well as sulfonamide antibiotics.

There are other types of sulfur containing substances

Elemental sulfur powder This is commonly used in gardening, and while irritation may occur from skin contact or inhalation, allergy has not been described.

Sulfates Some injectable drugs are sulfate compounds, for example heparin sulfate, dextran sulfate, morphine sulfate. The sulfates in soaps (such as sodium lauryl sulfate) are strong detergents and can irritate the skin or eyes, however sulfate itself does not cause allergic reactions. It is usually safe to use a sulfate when a person has a sulfonamide or a sulfite allergy.

Sulfite preservatives Commonly known as sulfur dioxide and metabisulfites, preservative numbers 220-228, sulfites are a group of compounds used to preserve flavour and colour and within food, inhibit bacterial growth, reduce spoilage, stop fresh food from spotting and turning brown and help preserve medication and increase shelf life. They are found most often found in wine, dried fruit, dried vegetables and sometimes sausages and salads. They can also occur naturally in low concentrations.  Sulfites can cause adverse reactions which are similar to allergies but do not involve the immune system (intolerances), most commonly asthma symptoms in those with underlying asthma, sometimes allergic rhinitis (hay fever) like reactions, occasionally urticaria (hives) and very rarely, anaphylaxis (allergic shock). Additional information on sulfite sensitivity is provided in a separate information article on the ASCIA website. There is no relationship between sulfite sensitivity and sulfonamide antibiotic allergy.

Non-antibiotic sulfonamide medicines. Some medicines contain sulfonamide molecules unrelated to sulfonamide antibiotics (such as some fluid tablets, diabetes tablets, some pain killers/arthritis tablets).
* It is important to note that these medicines do not need to be avoided by people because they are allergic to sulfonamide antibiotics; the allergy rarely if ever "crosses over".

Confirming the diagnosis

Skin allergy testing may be useful in some cases of suspected sulfonamide antibiotic allergy, but is not considered useful for assessing adverse reactions to sulfite preservatives. Skin testing may assist in distinguishing between allergic reactions to sulfonamide antibiotics and those to trimethoprim in individuals who have reacted to combination antibiotics such as Bactrim, Septrin or Resprim. These procedures are normally conducted by medical specialists (Allergists / Clinical Immunologists). 


The mainstay of management is avoidance. Those allergic to one sulfonamide antibiotic, should avoid all sulfonamide antibiotics. Since these antibiotics are not normally used in an emergency, wearing a MedicAlert bracelet is not routinely recommended. Desensitisation protocols to switch off antibiotic allergy temporarily are available should a sulfonamide antibiotic be the only suitable drug to use, but this is not possible in all cases of sulfonamide allergy, and this process does not work for sulfite preservative sensitivity.

© ASCIA 2010

The Australasian Society of Clinical Immunology and Allergy (ASCIA) is the peak professional body of Clinical Immunologists and Allergists in Australia and New Zealand.

Website: www.allergy.org.au

Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Postal address: PO Box 450 Balgowlah NSW Australia 2093


This document has been developed and peer reviewed by ASCIA members and is based on expert opinion and the available published literature at the time of review.  Information contained in this document is not intended to replace medical advice and any questions regarding a medical diagnosis or treatment should be directed to a medical practitioner. The development of this document is not funded by any commercial sources and is not influenced by commercial organisations.  


Content last updated January 2010

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