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Provided by Erica Glancy, MD

I developed a rash while taking amoxicillin for a childhood ear infection. I was told to avoid all penicillins because I might be allergic. Am I likely to have an allergy to penicillin? 

The penicillin family of antibiotics includes over a dozen chemically-related drugs, one common example being amoxicillin. Immediate allergic reactions to these antibiotics typically occur quickly after receiving a dose, and often include skin symptoms, such as hives. Labels of penicillin allergy are commonly attached in childhood with up to 10% of the population being labeled as penicillin allergic. Fortunately, over 90% of these individuals will actually be able to tolerate penicillin drugs. 

Why do so many people think they are allergic to penicillin if they really aren’t? 

Two potential reasons for the discrepancy between reported penicillin allergy and the ability to tolerate penicillin drugs are the mislabeling of side effects of penicillin as true allergies (e.g. stomach upset) and the occurrence of coincident events that aren’t actually due to allergy (e.g. hives related to the illness for which the antibiotic is being prescribed). Another very important factor is the loss of allergy with avoidance over time. Even in those with true allergy, over 90% will lose sensitivity over a 10 year period. 

Is there a way to find out if I am (still) allergic to penicillin? 

If history is concerning for penicillin allergy, an allergist may decide to perform penicillin skin testing in the office. Penicillin skin testing is highly sensitive, meaning that if testing is negative, there is a very high chance that the allergy is no longer present. 

What will happen during testing? Is it painful? 

Testing involves two steps, skin prick testing and intradermal testing. Skin prick testing, which is also called scratch testing, utilizes a device that barely penetrates the skin’s surface. Skin prick testing is typically not painful, producing only mild, momentary discomfort. If skin prick testing is negative, intradermal tests are placed. During this test, small amounts of different forms of penicillin are injected just beneath the skin using a small needle. For most people, this testing produces only minor discomfort. If tests are positive, there will be localized itching, redness, and swelling at the site where the test was performed. These reactions typically resolve within an hour. 

Is skin testing safe? Should I have my child tested if I am allergic? 

Penicillin allergy testing is a commonly performed procedure with minimal risk in properly selected patients. Testing is an option for both adults and children, as well as for other special populations if needed (e.g. pregnant women). Severe reactions to testing are rare, but because they can occur, testing is typically supervised by an allergist who is experienced in recognizing and treating any adverse reactions. Although skin testing is safe for most people, testing should only be performed if there is a history concerning for reaction. As opposed to some other allergies, there is no evidence that penicillin allergies are genetic, making screening unnecessary. 

Is penicillin skin testing accurate? How can I be sure I can take penicillins in the future? 

Penicillin allergy testing can accurately identify the approximately 9 in 10 patients who, despite a history of reaction, can take penicillin drugs safely. If testing is negative, over 99% of people will tolerate penicillin without immediate allergic reaction. While negative penicillin testing doesn’t eliminate the possibility of all adverse reactions, it specifically ensures that reactions of a severe, immediate nature are unlikely to occur. When testing is negative, an in-office challenge is typically performed to further ensure tolerance and provide confidence to the patient and caregivers that these drugs are safe. During a challenge, one or several doses of a penicillin drug are given by mouth followed by a period of observation. Following negative testing and challenge, patients are able to receive penicillin and penicillin-like antibiotics in the future. 

Can’t I just continue to avoid penicillins? Aren’t there other antibiotics that I can take instead? 

Penicillin antibiotics are one of the most frequently used classes of antibiotics in the world, as they are both effective and safe for the treatment of many infections. Alternate therapies (i.e. other antibiotics) are often associated with higher costs and/or greater risk of side effects. In addition, more frequent use of alternative antibiotics may lead to greater rates of severe drug-resistant infections which are in turn associated with increased costs and poorer patient outcomes.