What to avoid if you have a sulfa allergy

In the majority of cases, a person with a sulfa allergy will own experienced an allergic reaction to one or more of the following antibiotic drugs:

  1. Septra (sulfamethoxazole and trimethoprim)
  2. Bactrim (sulfamethoxazole and trimethoprim)
  3. Pediazole (erythromycin and sulfafurazole)

These reactions are not every that unusual and affect around 3 percent of every people. This is a rate similar to what is seen with other types of antibiotics, including penicillin.

Certain people appear to be at higher risk of sulfa allergy than others.

These include those who, for various reasons, own a suppressed immune system (such as organ transplant recipients and people with HIV/AIDS).

Sulfite and Sulfate Allergies

People will often error a sulfa allergy for a sulfite allergy. Sulfites are preservatives found in foods and medications. These include:

  1. Sodium sulfite
  2. Potassium bisulfite
  3. Sodium metabisulfite
  4. Sodium bisulfite
  5. Potassium metabisulfite

Sulfates are drugs containing sulfuric acid.

As with sulfites, sulfates may cause allergy, but the drugs are in no way related to sulfonamides or sulfa-allergy risk. These include medications such as:

  1. Albuterol sulfate used to treat bronchial spasms
  2. Chondroitin sulfate used to treat osteoarthritis
  3. Iron sulfate used to treat iron-deficiency anemia
  4. Codeine sulfate, an opioid drug used for pain relief

A Expression From Verywell

The nuances of a sulfa allergy can be tricky to tease out, even for some healthcare providers.

That's why it's significant to tell your doctor about any prior reaction you may own had to a sulfa medication (or any other drug for that matter). Sharing that information will make it easier for your doctor to prescribe a substitute that's less likely to cause an allergy.

It's significant to take every drug-related rash seriously, no matter how mild it may be.

What to avoid if you own a sulfa allergy

In some cases, continuing a sulfa-drug while having mild symptoms may cause those mild symptoms to become severe and life-threatening.

While sulfites can cause an ​allergy, there is no direct relationship between a sulfa and sulfite allergy—so someone with a sulfa allergy doesn't own to avoid sulfites (or vice versa).

Diuretics that do not contain a sulfonamide group (eg, amiloride hydrochloride, eplerenone, ethacrynic acid, spironolactone, and triamterene) are safe for patients with an allergy to sulfa. The evidence is contradictory as to whether a history of allergy to sulfonamide antibiotics increases the risk of subsequent allergic reactions to commonly used sulfonamide-containing diuretics (eg, carbonic anhydrase inhibitors, loop diuretics, and thiazides) (strength of recommendation: C, based on case series and poor quality case-control and cohort studies).

Are every sulfa drugs created equal?
Brian Crownover, MD, FAAFP
96 MDG Family Medicine Residency, Eglin Air Force Base, Fla

Historical bromides commonly drop by the wayside as better evidence becomes available.

Who would own thought 15 years ago that we would be promoting beta-blockers for patients with congestive heart failure?

Likewise, with closer inspection, we own learned that not every sulfa drugs are created equal. The stereospecificity due to the absence of aromatic amines in common diuretics means they are safe for patients with known sulfa antibiotic allergies. Given that diuretics are older agents and off-patent, with no company to take up their cause, no one has been willing to challenge outdated package insert warnings.

As clinicians who regularly work without a net, we are accustomed to prescribing medications in less than ideal circumstances.

What to avoid if you own a sulfa allergy

Thankfully, reasonable evidence is available to support what numerous of us are already doing—using cheap thiazides for patients despite a history of sulfa allergy.

Little research has been performed on sulfonamide antibiotic and sulfonamide diuretic allergic cross-reactivity. What we do know is that there are 2 classes of sulfonamides—those with an aromatic amine (the antimicrobial sulfonamides) and those without (eg, the diuretics acetazolamide, furosemide, hydrochlorothiazide, and indapamide).

Hypersensitivity reactions happen when the aromatic amine group is oxidized into hydroxylamine metabolites by the liver. Sulfonamides that do not contain this aromatic amine group undergo diverse metabolic pathways, suggesting that allergic reactions that do happen in this group are not due to cross-reactivity in sulfa-allergic patients. But that point is far from settled by the research.

A large retrospective cohort study using Britain’s General Practice Research Database identified 20, patients seen from through March who were prescribed a systemic sulfonamide antibiotic, and then at least 60 days later received a nonantibiotic sulfonamide (eg, thiazide diuretic, furosemide, oral hypoglycemic).1 Researchers reviewed records to determine whether patients described as having an allergic reaction to a sulfonamide antibiotic were at increased risk of having a subsequent allergic reaction to a sulfonamide nonantibiotic.

Patients were identified as being allergic using both narrow definitions (anaphylaxis, bronchospasm, urticaria, laryngospasm, or angioedema) and wide ones.

As only 18 patients out of the 20, patients were reported as having an allergic reaction using the narrow definition, analysis was based on the wide definition. Added to the wide category were asthma, eczema, and other “adverse” drug effects that were not specified by the author.

Using this wide definition, researchers identified allergies to sulfonamide antibiotics in patients.

What to avoid if you own a sulfa allergy

Of this group, 96 patients (%) had a subsequent reaction to a sulfonamide nonantibiotic, which included drugs from the loop and thiazide diuretic classes (including bumetanide, chlorothiazide, furosemide, hydrochlorothiazide, indapamide, and torsemide). It was unclear if any patients taking a carbonic anhydrase inhibitor experienced an allergic reaction. For comparison purposes, of the 19, patients who were not identified as having an allergy to a sulfonamide antibiotic, again using the wide definition, (%), had a subsequent allergic reaction to a sulfonamide nonantibiotic, for an unadjusted odds ratio of (95% confidence interval [CI], –).

When the results were adjusted for age, sex, history of asthma, use of medications for asthma or corticosteroids, the adjusted odds ratio for individuals experiencing an allergy to a nonantibiotic sulfonamide in those persons with a history of allergy to a sulfonamide antibiotic was (95 % CI, –).

What to avoid if you own a sulfa allergy

Of note, the adjusted odds ratio for the occurrence of a penicillin allergy in a patient with a history of sulfonamide antibiotic allergy was significantly higher at (95% CI, –).

Some limitations of the study included uncertainty of cause and effect of prescribed medications and subsequent reactions, possible inconsistency of physician diagnosis and coding, and lack of precision in the diagnosis of allergic reactions. There is also the possibility of “suspicion bias,” where patients with a history of allergies may be more closely monitored for subsequent reactions than nonallergic patients.

Sulfa allergy: Which medications should I avoid?

Medically reviewed by Final updated on Dec 4,

Someone who has a sulfa allergy can react to some medications that contain sulfa.

Other medications that may cause a reaction

Other types of sulfa medications may trigger a reaction in some people who own a sulfonamide antibiotic allergy:

  1. Sulfasalazine (Azulfidine), used to treat Crohn’s disease, ulcerative colitis and rheumatoid arthritis
  2. Dapsone, used to treat leprosy, dermatitis and certain types of pneumonia

Keep in mind that if you own a reaction to a sulfonamide antibiotic, you may still be capable to take other sulfonamide medications without having a reaction.

Sulfonamide antibiotics that can cause a reaction

Antibiotics containing chemicals called sulfonamides can trigger a reaction if you own a sulfa allergy.

These antibiotics include combination drugs:

  1. Sulfamethoxazole-trimethoprim (Septra, Bactrim)
  2. Erythromycin-sulfisoxazole

Sulfonamide medications that may be OK

  1. Certain diabetes medications — glyburide (Glynase, Diabeta) and glimepiride (Amaryl), for example
  2. The migraine medication sumatriptan (Imitrex)
  3. Some nonsteroidal anti-inflammatory drugs, such as celecoxib (Celebrex)
  4. Certain «water pills» (diuretics), such as furosemide (Lasix) and hydrochlorothiazide (Microzide)

An allergy to sulfonamide medications is diverse from having an adverse reaction to wine or food that contains sulfites.

Having a reaction to sulfites in something you eat or drink doesn’t mean you’ll be allergic to sulfonamide medication.

If you own HIV/AIDS, you may own an increased sensitivity to sulfonamide medications. Always tell your doctor about your sensitivities to medication.

There are no diagnostic tests for sulfa allergy. However, sulfa desensitization might be an option, especially if medication containing sulfamethoxazole is needed.

© Mayo Foundation for Medical Education and Research (MFMER).

What to avoid if you own a sulfa allergy

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Stevens-Johnson syndrome is a rare but serious disorder that affects the skin, mucous membrane, genitals and eyes.

The mucous membrane is the soft layer of tissue that lines the digestive system from the mouth to the anus, as well as the genital tract (reproductive organs) and eyeballs.

Stevens-Johnson syndrome is generally caused by an unpredictable adverse reaction to certain medications.

What to avoid if you own a sulfa allergy

It can also sometimes be caused by an infection.

The syndrome often begins with flu-like symptoms, followed by a red or purple rash that spreads and forms blisters. The affected skin eventually dies and peels off.

Stevens-Johnson syndrome is a medical emergency that requires treatment in hospital, often in intensive care or a burns unit.

Treatment aims to identify the underlying cause, control the symptoms and prevent complications.

Erythema multiforme is a similar, but less severe, skin reaction that’s generally caused by infection, particularly herpes viral infections, and chest infections.

Medications to Avoid

People with a known sulfa allergy should always check with their doctor before starting a new medication.

What to avoid if you own a sulfa allergy

This is especially true for those who own had a previous severe reaction.

In addition to oral antibiotics, topical sulfonamides should be avoided. These include:

  1. Sulfacetamide eye drops, shampoos, or creams
  2. Silver sulfadiazine ointments used to treat burns
  3. Sulfanilamide vaginal preparations

Similarly, the oral drug Azulfidine (sulfasalazine), used to treat inflammatory bowel disease and rheumatoid arthritis, should be avoided.

Keep in mind that the risk of cross-reactivity to non-antibiotic sulfonamides is low.

This means that it's generally safe to take the following drugs:

  1. Diuretics (water pills) such as HCTZ (hydrochlorothiazide) and Lasix (furosemide)
  2. Oral sulfonylureas-class drugs used to treat diabetes
  3. Celebrex (celecoxib), a COX-2 inhibitor used to treat arthritis and pain


The first-line of treatment of a sulfa allergy is typically the termination of the suspected drug.

Anaphylaxis requires immediate epinephrine use and medical care.

Stevens-Johnson syndrome or toxic epidermal necrolysis are also potentially life-threatening conditions that require immediate medical evaluation; in severe cases, management in a burn unit may be required.

In milder cases where a sulfa drug is considered essential to the treatment of an infection, an allergist or other qualified physician may supervise the istration of smaller doses and gradually increase them as the drug is better tolerated.


There's no validated skin or blood test available to diagnose a sulfa allergy.

The diagnosis is generally made on careful review of the suspected reaction and history of current and previous medication use.


The symptoms and severity of a sulfa allergy can vary but generally involve the appearance of a widespread rash. Occasionally a photosensitive rash may develop, meaning that a rash will happen in areas exposed to sunlight or other UV light while on the medication.

Other serious manifestations of a sulfa allergy include: