Q: I'm often asked if I am allergic to penicillin. How do I know for sure?
A: The label of penicillin allergy is commonly attached in childhood where 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. Consequently, although approximately 10 percent of the population is labeled as being allergic to penicillin, more than 90 percent of these individuals actually are negative on allergy testing and can tolerate penicillin. Overall penicillins are the safest and most effective antibiotics for many infections, and therefore it is important to find out if a patient is really penicillin allergic.
Penicillin allergy can be evaluated by an allergist, who will obtain a careful history and perform skin testing. This test involves pricking the skin with two forms of penicillins (each of which mimics the forms of penicillin that are found in the blood when a patient takes the drug) and a subsequent intradermal test (placing a small amount of each form of penicillin 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 patient is not at risk of having a serious immediate reaction and penicillins can be used thereafter.
— Dr. Russell Walker, The Allergy & Asthma Group of Galen; member, Chattanooga-Hamilton County Medical Society