Understanding sulfa allergy, sulfites and sulphur
Some drugs contain certain chemicals called sulfonamides, which can cause a bad reaction or allergic reaction in some people.
Usually, people know that they are allergic to sulfa drugs from a bad reaction previously, typically from antibiotics that contain sulfonamides. Not all sulfa drugs cause the same reaction, even if you have a sulfa allergy or intolerance. Most sulfa drug reactions are from antibiotics.​1–3​
There is no reliable test for sulfa allergy.
Sulfonamides were the first antibiotics ever introduced in 1936. The terms sulfur, sulfite, sulfate, and sulfonamide replace sulphur, sulphite, sulphate and sulphonamide, terminology-wise, in Australia since 1999.
Drugs that contain sulfonamides include:
- Erythromycin-sulfisoxazole (antibiotics)
- Sulfamethoxazole-trimethoprim (Septra, Bactrim, Resprim) (antibiotics)
- Sulfasalazine (Azulfidine, Salazopyrin, Pyralin) (Crohn’s disease, ulcerative colitis and rheumatoid arthritis treatment, a combination of sulfapyridine (antibiotic) and a salicylate)
- Dapsone (Aczone) (leprosy, dermatitis and pneumonia treatment)
- Glyburide (Glynase, Diabeta) and glimepiride (Amaryl) (diabetes treatments)
- Celecoxib (Celebrex) (nonsteroidal anti-inflammatory drug)
- Sumatriptan (Imitrex) (migraine treatment)
- Furosemide (Lasix) and hydrochlorothiazide (Microzide) (diuretics)
- Sulfadiazine (tablets, injection or cream antibiotic for preventing and treating burn infections)
- Sulfadoxine (malaria treatment)
- Sulfacetamide (antibiotic eye drops)
Sulfa drug allergy or intolerance symptoms
- Rash
- Hives
- Itching eyes
- Itching skin
- Problems breathing
- Swollen face
- Headache
- Sleep problems
- Cloudy urine (crystalluria)
- Low blood counts
- Red, swollen round patches on skin that start between 30 minutes and eight hours after starting the drug
- Steven-Johnson syndrome – skin blisters and peels off, possibly life-threatening
What is sulfonamide drug hypersensitivity syndrome?
This syndrome is the collection of rash, fever and organ problems that start 1-2 weeks after starting on a sulfonamide drug.
Treatments for sulfa drug allergy
- Antihistamines
- Corticosteroids
- Epinephrine in the case of anaphylaxis
Guidelines for those with sulfa allergy or intolerance​4​
The severity of the reaction should guide you, so if you had a serious anaphylactic, life-threatening allergic reaction, then sulfa antibiotics should be avoided unless it is an emergency and there is no other option.
If the allergy also includes non-antibiotics that contain sulfonamides, again, do not use unless absolutely necessary.
The chances of cross-reactivity are small between non-antibiotic drugs and antibiotics containing sulfonamide, so if no threat exists, start with low doses and monitor for reactions. Advise all healthcare providers of your sulfa drug allergy.
If you have had an allergic reaction to Bactrim, Resprim or Septrin, you won’t know if the allergy was to sulfamethoxazole or to trimethoprim, therefore it’s best to avoid trimethoprim (Alprim, Triprim) as well as sulfonamide antibiotics.
If need be, wear a medical bracelet.
What are sulfites then?
Sulfites are preservatives found in food and drinks like dried fruit and wine. This food sensitivity is not the same as being allergic to sulfa drugs. Sulfites might cause asthma or flushing of the cheeks and neck, and, unusually, more serious allergic reactions, including anaphylaxis.
Sulfa drugs and sulfites are not the same thing, but both contain sulphur-containing compounds, so if you’re overall sensitive to sulphur, you may find both cause issues.
What is sulphur/sulfur?
Wording matters here, though it might seem very confusing – that is fair! Sulphur is a building block of life and it is not possible to be allergic to sulphur itself. We need it to survive.
But, the biological pathways that use sulphur may be slow-moving, causing a build-up of sulphur in the body and thus symptoms to appear. You may find it difficult to tolerate high-sulphur foods such as onion, garlic, broccoli, cauliflower, and other brassica vegetables, preservative numbers 220-228, sodium lauryl sulfate in soaps and shampoos, sulfites in wine, sulfa medications, medicines, gardening with elemental sulphur powder, and other things that contain sulphur-related molecules – but maybe not.
This overload can result in certain substances being higher than ideal in your system and reduce the effectiveness of your immune system, resulting in frequent or chronic infections, including vaginal and urinary tract infections.
Any reaction here is not an allergy as such, but an overload, and you should seek professional help to get your pathways moving again.
References
- 1.Strom BL, Schinnar R, Apter AJ, et al. Absence of Cross-Reactivity between Sulfonamide Antibiotics and Sulfonamide Nonantibiotics. N Engl J Med. Published online October 23, 2003:1628-1635. doi:10.1056/nejmoa022963
- 2.Johnson KK, Green DL, Rife JP, Limon L. Sulfonamide Cross-Reactivity: Fact or Fiction? Ann Pharmacother. Published online February 2005:290-301. doi:10.1345/aph.1e350
- 3.Slatore CG, Tilles SA. Sulfonamide hypersensitivity. Immunology and Allergy Clinics of North America. Published online August 2004:477-490. doi:10.1016/j.iac.2004.03.011
- 4.Ponka D. Approach to managing patients with sulfa allergy: use of antibiotic and nonantibiotic sulfonamides. Can Fam Physician. 2006;52(11):1434-1438. https://www.ncbi.nlm.nih.gov/pubmed/17279201
