Allergies to sulfa drugs are common. Whether caused by a true allergy or drug intolerance, sulfa reactions affect up to 6% of people. The rate is similar to responses to other types of antibiotics, including penicillin.
This article explains sulfa allergy symptoms, causes, diagnosis, and treatment. It also covers how to decipher between sulfa allergy and sulfite allergy.
What Is a Sulfa Allergy?
Sulfa allergies are allergic-type reactions to sulfonamide drugs. If someone is sensitive to sulfa, the most common reactions manifest on the skin as rashes. However, symptoms can also be more severe.
Sulfonamides are one of the earliest developed antimicrobial drugs. They are used less frequently than in the past because safer, more effective medications have replaced them. However, they still have uses today, especially for treating certain infections, including:
Pneumocystis pneumonia (PCP) caused by the fungus Pneumocystis jirovecii Uncomplicated cystitis (bladder inflammation and irritation) Stenotrophomonas maltophilia (S. maltophilia) infection, a bacteria that can live in IV fluids, respiratory mucus, and urine
The most common sulfa drug associated with sulfa allergy is sulfamethoxazole-trimethoprim (Bactrim, Septra, and others).
Sulfa vs. Sulfite Allergy
While they sound similar, sulfa drug allergy and sulfite allergy are not the same things. As mentioned earlier, a sulfa drug is derived from the sulfonamide molecule.
On the other hand, sulfites are compounds containing sulfuric acid used as preservatives in packaged foods and wine. They can cause reactions in some people but are not related to sulfonamides. As such, you don’t need to avoid sulfites if you have a sulfa allergy.
You’ll find sulfites in the following products:
Baked goodsDried fruitsCondimentsShrimpWines and beer
Reactions to sulfites include worsening asthma symptoms, anaphylaxis (a severe, life-threatening reaction), and hives.
Sulfur dioxidePotassium bisulfitePotassium metabisulfiteSodium bisulfiteSodium metabisulfiteSodium sulfite
Sulfa Allergy Symptoms
The symptoms and severity of a sulfa allergy can vary from mild to life-threatening. Call a healthcare provider if you develop any signs of a sulfa allergy, even if your symptoms are mild. Seek emergency care if symptoms are severe and rapidly progressing.
In some cases, continuing a sulfa drug while having mild allergy symptoms may eventually result in severe and life-threatening effects.
Common
Common symptoms of sulfa allergy are often limited to the skin and may include:
Maculopapular eruption (flattened, red rash) Pruritus (itchy skin) Urticaria (hives) Angioedema (swelling of the face, hands, and other tissues)
Rashes can get worse with sun exposure.
Severe
Certain people may develop anaphylaxis, a potentially life-threatening, whole-body allergy that can lead to shock, coma, respiratory or heart failure, and death if left untreated.
Anaphylaxis usually occurs within minutes to several hours of a dose.
Swelling of the throat or tongue Difficulty swallowing Difficulty breathing or rapid breathing Wheezing Lightheadedness or fainting Racing heart or irregular heartbeat Nausea or vomiting Severe rash or hives Blue-colored skin A feeling of impending doom
Other severe reactions can take longer to develop. For example, Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) may take up to eight weeks after exposure to a drug (usually between four and 30 days) to develop. With both of these conditions, large areas of skin will blister and peel, posing the risk of severe dehydration, shock, and death if left untreated.
Sulfa Allergy Causes
Certain people are at a higher risk of sulfa allergy than others. These include people who are immunocompromised, especially those with advanced HIV infection.
Antibiotics
All sulfa drugs have the potential to induce an allergic reaction. However, research suggests that antibiotic sulfonamides (used to treat bacterial infections) are more likely to trigger an allergic reaction than other sulfa drugs.
Sulfa antibiotic drugs that may cause an allergic reaction include:
Sulfadiazine Sulfanilamide Sulfamethoxazole (Bactrim or Septra)
Topical Creams
In addition, topical sulfa antibiotic medications can cause a reaction in hypersensitive people. These include:
Sulfacetamide shampoos, creams, and eye drops Silver sulfadiazine (Silvadene) ointments used to treat burns Sulfanilamide vaginal preparations
Non-Antibiotic Sulfonamides
Many people with a sulfa allergy can tolerate non-antibiotic sulfonamides because the risk of cross-reactivity (an allergic reaction that occurs when proteins in a substance are similar to an allergen) is lower. Even so, it is still possible to react to these medications in hypersensitive people.
Non-antimicrobial sulfa drugs include:
Celebrex (celecoxib) is a COX-2 inhibitor used to treat arthritis Diamox (acetazolamide), is used to treat epilepsy, intracranial hypertension (spinal fluid pressure in the brain), glaucoma, and heart failure Diuretics like Bumex (bumetanide), Microzide (hydrochlorothiazide), Lasix (furosemide), and Thalitone (chlorthalidone) Migraine medications like Frova (frovatriptan), Imitrex (sumatriptan), and Relpax (eletriptan) Oral sulfonylureas-class drugs like Amaryl (glimepiride), Glynase (glyburide), and Glucotrol (glipizide) used to treat type 2 diabetes Azulfidine (sulfasalazine) used to treat Crohn’s disease, ulcerative colitis, and rheumatoid arthritis
G6PD
In addition, people with a glucose 6 phosphate dehydrogenase (G6PD) deficiency (a lack of enough of a specific red blood cell enzyme) are at risk of developing hemolytic anemia. This type of anemia occurs when red blood cells break down too soon.
Exposure to certain blood-related things, including sulfa drugs, can trigger hemolytic anemia in people with G6PD. This reaction is entirely different from an allergy.
Diagnosis
While healthcare providers can diagnose some drug allergies through allergy testing, that is not the case for sulfa drugs. Instead, a diagnosis usually relies on carefully examining symptoms and a review of your current and previous medication use.
However, topical medications and non-antimicrobials can also cause reactions. In addition, sulfa drugs can trigger hemolytic anemia in those with G6PD deficiency.
In some cases, an allergist (an allergy, asthma, and immunology specialist) may recommend an oral drug challenge. This test involves taking the medication suspected of causing a reaction under the supervision of a healthcare provider. However, this may be too dangerous if your past response was severe.
Some experts believe this type of testing should be the standard for suspected sulfa drug allergies in immunocompromised people due to their high antibiotic usage. However, this is not yet the norm.
Treatment
The first-line treatment for a sulfa allergy is stopping the suspected drug. However, in cases of suspected anaphylaxis, drug desensitizations can be performed in which small amounts of medication are slowly titrated upwards until a full dose can be tolerated.
For safety, this must be done under physician supervision with appropriate staffing and supplies to treat severe anaphylaxis. As long as people stay on the medication(s) that they have been desensitized to, they should not react. If they stop the medication, they would need to undergo another desensitization prior to receiving the medication again.
Unfortunately, Stevens Johnson Syndrome reactions and Toxic Epidermal Necrolysis reactions cannot usually be treated this way and this approach is not recommended for them.
Treatment for more severe reactions might include:
Epinephrine injection (EpiPen) hormone to halt an anaphylactic reaction Antihistamines, drugs that block the chemical, histamine Corticosteroids, drugs that reduce inflammation Pain medications Intravenous hydration (IV therapy)
SJS and TEN may also require burn center care.
Prevention
Always check with a healthcare provider before starting a new medication if you have a known sulfa allergy. This precaution is especially crucial if you had a previous severe reaction to sulfa drugs.
Ideally, a healthcare provider will document the specific sulfa drug and the specific reaction rather than listing an allergy to a whole class of drugs. Doing so helps prevent future use, even if sold under a different trade name.
Once you identify the drug that caused the reaction, it’s essential to record it. You may even choose to wear a medical bracelet identifying your allergy. In addition, some people who have had severe reactions keep documentation on them to avoid receiving the drug in the future.
Summary
Sulfa allergies are an allergy to a group of medications containing sulfonamides. It is not the same as a sulfite allergy, an allergy to a food preservative. The most common symptom is an itchy rash. However, more severe reactions, including anaphylaxis, Stevens-Johnson syndrome (SJS), and toxic epidermal necrolysis (TEN), can also occur.
A Word From Verywell
The nuances of a sulfa allergy can be tricky to tease out, even for some healthcare providers. That’s why it’s important to tell your healthcare provider about any prior reaction you may have had to a sulfa medication (or any other drug for that matter). Sharing that information will make it easier for your healthcare provider to prescribe a substitute for you that is less likely to cause an adverse reaction.
