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Sulfa Drug Allergy

Sulfa Medication Allergies


Updated June 03, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

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Updated June 03, 2014

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.

Don't Miss Page 2: Which Medications to Avoid if You Have A Sulfa Allergy

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