What You Should Know about Penicillin Allergy

What You Should Know about Penicillin Allergy

Penicillins are widely used anti-biotics that have important roles in treating bacterial infections. The label of penicillin allergy is commonly attached in childhood, a time when common childhood infections may themselves contribute to or be confused with allergy. In addition, even in those with true allergy, over 90 percent will lose this tendency over a 10-year period. So, although about 10 percent of the population is labeled as being allergic to penicillin, over 90 percent of these individuals test negative for penicillin allergy and can take the drug. 

Penicillins are the safest and most effective antibiotics for many infections. Therefore, it’s important for people who’ve had a bad reaction to penicillin to find out if they really are penicillin allergic.

Symptoms of Penicillin Allergy  
Immediate allergic reactions to penicillins typically occur quickly (less than an hour) after receiving a dose of the medication. And they often occur in people who have tolerated previous courses of penicillin without issue. Symptoms often involve the skin and include hives (a raised, itchy rash; also known as welts or urticaria) and swelling (also known as angioedema), which commonly occurs around the face and extremities (the hands and feet). Treatment of these reactions usually involves an antihistamine and sometimes an oral or injected corticosteroid. 

In rare cases, more serious reactions that suggest anaphylaxis can occur. These include
• Swelling of the tongue, throat, and lips
• Respiratory symptoms, such as difficulty breathing, coughing, chest tightness, and wheezing
• Light-headedness or loss of consciousness (which is caused by low blood pressure)

Although about 10 percent of the population is labeled as being allergic to penicillin, over 90 percent of these individuals test negative for penicillin allergy.

These symptoms require immediate treatment with epinephrine, which can be given at home with an autoinjector if available, at the nearest emergency room, or by calling 911. Additional treatments may include albuterol (to treat respiratory symptoms), IV fluids, and corticosteroids.

Penicillin Allergy Diagnosis  
Penicillin allergy can be evaluated by an allergist or immunologist, who will obtain a careful history and perform skin testing. This testing includes a skin prick test, which involves pricking the skin with two forms of penicillin, followed by an intradermal test, where a small amount of each form of penicillin is placed just under the skin. 

If these tests are negative, it is very unlikely that a penicillin allergy is present. In many instances, after negative testing, a dose of an oral penicillin is also given, followed by an observation period. If there is no reaction, the person is not at risk of having a serious immediate reaction and can take penicillins thereafter. The testing typically takes about two to three hours.

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In cases of a positive penicillin test, either the skin prick or intradermal test will produce a red, raised bump, signifying the presence of an allergy to the medication. People who test positive for penicillin allergy need to avoid penicillins, and, therefore, will need to take a different antibiotic to treat infections. If a situation occurs in which a penicillin is needed, a desensitization procedure can be performed under the care of an allergist or immunologist to temporarily allow the drug to be used.


What is penicillin?
Penicillin was first discovered by Alexander Fleming in 1928, and it continues to be one of the most important antibiotics today. The penicillin family of antibiotics contains over 15 chemically related drugs (for example, penicillin, ampicillin, amoxicillin, amoxicillin-clavulanate, methicillin) that are given by mouth or injection for the treatment of many bacterial infections. It is one of the most frequently used classes of antibiotics in the world.

I was told that I was allergic to amoxicillin; do I still need to see an allergist or immunologist?
Amoxicillin is in the same family of antibiotics as penicillin. An allergist or immunologist can review your history and perform skin testing to help you understand if you are still allergic to amoxicillin. This skin testing is similar to penicillin skin testing.

Is skin testing painful?
A skin prick test, which checks for immediate allergy, is the first step in skin testing. Skin prick testing is usually not painful and involves needles that barely penetrate the skin’s surface. You won’t bleed or feel more than mild, momentary discomfort. Intradermal skin testing is the second part of the evaluation, and it involves injecting the skin. The test, if positive, will cause local itching and redness with swelling at the site where the test is performed. These reactions usually resolve in an hour or so. 

Is penicillin allergy genetic?
There is no predictable pattern to inheritance of penicillin allergy. You do not need to avoid penicillin if a family member is allergic to penicillin or to drugs in the penicillin family.

Source: American Academy of Allergy, Asthma & Immunology, aaaai.org

This article was originally published in Coping® with Allergies & Asthma magazine, Spring/Summer 2017.