Am I Allergic to Penicillin? Probably Not

by Russell Traister, MD, Bloomfield Allergy

Are you one of almost 10 percent

of people who believe they have an allergy to penicillin, a common antibiotic used to treat many common infections? You are likely not alone as it is the most commonly reported drug allergy. It turns out that up to 19 out of 20 patients who believe they have a penicillin allergy, in fact, do not. This can seem inconsequential if you are someone who is not sick often or rarely requires antibiotics, but carrying this diagnosis long-term could lead to issues when you are older or require hospitalization. Older patients often carry this diagnosis from childhood and have no recollection of why they were labeled penicillin allergic. For many infections, a penicillin or related antibiotic is considered the first-line treatment. Treatment with alternative agents could lead to less efficient treatment of an infection and can also lead bacteria to develop resistance to treatment. In fact, patients labeled with a penicillin allergy have a 70 percent higher risk of developing methicillin-resistant Staphylococcus aureus (MRSA) infections. In addition, many alternative agents are costly and can have significant side effects.

The reason for the high rate of misdiagnosis of penicillin allergy is multifactorial. Allergists are primarily concerned about immediate, IgE-mediated, anaphylactic reactions, as these can be life threatening and require immediate treatment. This type of reaction could include diffuse hives, swelling, shortness of breath, wheezing, vomiting, diarrhea, and syncope. If this reaction occurs, strict avoidance of the offending drug is necessary. Despite this, patients with a true life threatening allergy to penicillin are likely to outgrow it over time, with up to 90 percent being able to tolerate penicillin after 10 years of avoidance. Adding to the confusion is that many viral infections can cause rashes that can be easily confused with reactions to medication, and this often leads to misdiagnosis of penicillin allergy. However, viral rashes or even delayed-onset drug rashes (without other symptoms) can be bothersome. Luckily, they can often be treated with steroid medications or left to resolve on their own. These reactions do not require future avoidance of the offending agent, if a drug was implicated. Lastly, patients could also simply have intolerances to penicillin, such as diarrhea, which can be common with antibiotic treatment.

It is important to discuss any drug allergies, including penicillin, with your allergist. After discussion, they may decide to perform skin testing to penicillin. If negative, the last step is to challenge the patient to an oral dose of penicillin to ensure that it is tolerated. If so, your allergist will remove penicillin from your allergy list, and you will be free to receive such antibiotics in the future without concern for reaction.