What is sulfa allergy?
"Sulfa allergy" is a term used to describe adverse drug reactions 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 today are used much less frequently given their common side effects. Common sulfa antibiotics include Septra®, Bactrim® and Pediazole®.The antibiotic sulfonamides are different structurally from the non-antibiotic sulfonamides, and appear to be much more likely to result in allergic reactions. Many of the sulfa non-antibiotics, therefore, do not cause problems in people with sulfa antibiotic allergy.
How common is sulfa allergy?
The overall incidence of adverse drug reactions to sulfa antibiotics is approximately 3%, similar to other antibiotics such as penicillin. Certain groups appear to be at higher risk for sulfa allergy, including those that metabolize these medications more slowly and those with immune problems such as AIDS.What symptoms are common in sulfa allergy?
Skin reactions. Skin reactions are the most common adverse reactions to sulfa medications, ranging from various benign rashes to life-threatening Stevens-Johnson syndrome and toxic epidermal necrolysis. Hives and increased sensitivity to sunlight (photosensitivity) are also possible. There is a possibility that if the sulfa medication is continued despite a mild rash occurring, the rash could progress to a more severe form of skin reaction.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.
How is sulfa allergy diagnosed?
There is no skin test or blood test available to diagnose sulfa allergy. Therefore, the diagnosis is made when a person, who is taking a sulfonamide medication, experiences symptoms consistent with those seen in sulfa allergy.How is sulfa allergy treated?
In most cases, if a person is experiencing an adverse reaction to a sulfa medication, that medication should be stopped. The symptoms of the reaction may need to be treated, especially in those experiencing Stevens-Johnson syndrome or toxic epidermal necrolysis.In some cases, in which a sulfa medication is needed to treat certain infections, a person can be desensitized to the medication. This is done by initially giving very small amounts of the medication, with increasing amounts given over a period of time so that the medication is tolerated. The sulfonamide medication can also be cautiously continued despite the adverse side effect. These patients should be treated by an allergist experienced in the management of drug allergies.
What medications should sulfa-allergic patients avoid?
The following list is by no means comprehensive. People with allergy to sulfa or sulfonamide-related medications should always check with their doctor or pharmacist prior to starting any new medications.Sulfa antibiotics. In people with adverse reactions to sulfonamide antibiotics, all other sulfonamide antibiotics should be avoided. These include trimethoprim-sulfamethoxazole (Septra®, Bactrim® and generics), sulfadizine, sulfisoxazole, and dapsone. Topical sulfa antibiotics, such as sulfacetamide eye drops/shampoos/creams, silver sulfadiazine cream, and sulfanilamide vaginal preparations.
Diuretics (water pills). The risk for sulfa-containing diuretic medications causing reactions in sulfa-allergic patients is low. According to product labeling, medications such as hydrochlorothiazide (generic forms and in combination with other blood pressure medications) should not be given to sulfa-allergic patients, while medications such as furosemide (Lasix®) can be used. If a diuretic is needed in a sulfa-allergic patient, it is recommended that the first dose of the medication be given under medical supervision.
Sulfonylureas. Oral medications used for the treatment of diabetes, called sulfonylureas (such as chloropropamide, glyburide, and glipizide), are structurally similar to sulfonamides. While there are a few reports of these medications causing problems in sulfa-allergic patients, these medications are generally tolerated.
Celebrex®. Celecoxib (Celebrex®), a popular COX-2 inhibitor used for the treatment of arthritis and pain control, is a sulfonamide non-antibiotic medication. Although there have been no reports of sulfa-allergic patients reacting to Celebrex®, it is a theoretical concern, so the recommendation is that sulfa-allergic patients avoid this medication.
Sulfasalasine. Sulfasalasine is a sulfonamide that is related to aspirin, and is used for inflammatory bowel disease and rheumatoid arthritis. This medication should not be used in people with sulfa allergy.
Imitrex®. Sumatriptan (Imitrex®), used for the treatment of migraine headaches, is related structurally to sulfonamides, although there is no evidence that people with sulfa allergy are at increased risk for reactions from this medication.
Zonisamide. Zonisamide is a sulfonamide medication used for the treatment of seizures. It has been associated with severe skin reactions, those typically seen with sulfa reactions. This medication should not be used in sulfa-allergic patients.
Want to keep learning? Find out if you should also be concerned about sulfite allergy.
Sources:
- 1. Choquet-Kastylevsky G, et al. Allergic Adverse Reactions to Sulfonamides. Current Allergy and Asthma Reports. 2002;2:16-25.
- 2. Allen J. Which Medications to Avoid in Patients with Sulfa Allergy? Prescriber's Letter. July 2000.
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