What is a Sulfa Allergy?
Sulfa allergy is a term used to describe an adverse drug reaction to sulfonamides, a group of drugs that includes both antibiotics and nonantibiotics.
The antibiotic sulfonamides are more likely to result in allergic reactions than nonantibiotic sulfonamides.
In fact, you may be surprised to learn that many of the nonantibiotic sulfonamides do not cause problems in people with sulfa antibiotic allergy — a common misconception.
In the majority of cases, a person with a sulfa allergy has experienced an allergic reaction to one of these common sulfa-containing antibiotics:
- Septra (sulfamethoxazole and trimethoprim)
- Bactrim (sulfamethoxazole and trimethoprim)
- Pediazole (erythromycin and sulfafurazole)
These adverse drug reactions to sulfa antibiotics are actually not that uncommon, affecting approximately three percent of people. This is similar to other antibiotics, such as penicillin.
In addition, 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.
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.
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.
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 managing drug allergies.
Medications to Avoid
People with an allergy to sulfa (sulfonamide) should always check with their doctor prior to starting any new medication.
That being said, for people with adverse reactions to sulfonamide antibiotics, all other sulfonamide antibiotics should be avoided. These include trimethoprim-sulfamethoxazole (Septra®, Bactrim®, and generics), sulfadiazine, sulfisoxazole, and dapsone.
Topical sulfa antibiotics, such as sulfacetamide eye drops/shampoos/creams, silver sulfadiazine cream, and sulfanilamide vaginal preparations should also be avoided.
Sulfonamides that are not antibiotics are another story, as the research suggesting possible cross-reactivity is quite limited.
For instance, examples of nonantibacterial sulfonamides that may be OK to take even if a person had a reaction in the past to sulfa, include:
- Some diuretics (water pills), such as HCTZ ( hydrochlorothiazide ) and Lasix (furosemide)
- Some oral medications for diabetes like the sulfonylureas (for example, Amaryl which is glimepiride)
- Celebrex (celecoxib) is a COX-2 inhibitor used for the treatment of arthritis and pain control.
On the other hand, Azulfidine (sulfasalazine) 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, as sulfasalazine is structurally related to antibiotic sulfonamides — an exception, so to speak.
Sulfa vs. Sulfite Allergy
Many people assume that if they are allergic to sulfa-containing drugs, they are also allergic to sulfite, a preservative agent in foods and medications. But, this is not necessarily true.
Sulfites are common preservatives used in various foods and medications. Sulfites have been used for centuries, mainly as food additives, but can also occur naturally in foods such as fermented beverages and wines.
Examples of sulfites include:
- sodium sulfite
- sodium bisulfite
- sodium metabisulfite
- potassium bisulfite
- potassium metabisulfite
Sulfites are best known to cause worsening breathing problems in people with asthma when foods or beverages containing sulfites are eaten (although this is not a common phenomenon). In addition, there are rare reports of sulfite-induced anaphylaxis.
Sulfates vs. Sulfur
Likewise, sulfates are salts of sulfuric acid and are commonly used in the making of various drugs, such as albuterol sulfate, iron sulfate, chondroitin sulfate, and codeine sulfate.
While allergic reactions to these medications are possible, it’s not likely that it’s due to the sulfate group. In fact, there does not appear to be any reason for people with sulfa or sulfite allergies to avoid medications that contain a sulfate salt.
Finally, sulfur is a chemical element that is used in the production of countless pharmaceutical and commercial chemicals and is present in (and responsible for the names of) sulfa drugs, sulfite preservatives, and sulfates.
Sulfur is too small, as an element, to cause allergic reactions by itself; therefore, there does not appear to be a reason for people with sulfa and/or sulfite allergy to specifically avoid sulfur-containing compounds.
All in all, the nuances of a sulfa allergy can be tricky, even for some healthcare providers to tease out. That is why it s important to report any prior reaction you have had to a sulfa medication (or any medication) to your doctor. It s also best if you can describe the reaction, like whether it was mild or severe.
Joint Task Force on Practice Parameters et al. Drug allergy: an updated practice parameter. Ann Allergy Asthma Immunol. 2010 Oct;105(4):259-73.