Allergy Facts and Myths

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• Penicillin allergies are the most frequently reported allergies, but greater than 90% are inaccurate (1)
• Not all reactions that happen after taking penicillin are allergic reactions: penicillin intolerances or viral exanthems may be recorded as allergies, and penicillin allergy wanes over time
• Inaccurate labels limit your antibiotic options and can contribute to the development of superbugs. They are also associated with worse outcomes in hospital
• There are not enough allergy specialists to verify everyone's penicillin allergy 
• Reassessing an incorrect allergy label has many potential benefits

Our goal is to help you estimate your true risk of penicillin allergy, and guide whether or not it is safe to challenge it!

1.  David A. Khan, Aleena Banerji, Kimberly G. Blumenthal, Elizabeth J. Phillips, Roland Solensky, Andrew A. White, Jonathan A. Bernstein, Derek K. Chu, Anne K. Ellis, David BK. Golden, Matthew J. Greenhawt, Caroline C. Horner, Dennis Ledford, Jay A. Lieberman, John Oppenheimer, Matthew A. Rank, Marcus S. Shaker, David R. Stukus, Dana Wallace, Julie Wang, Drug Allergy: A 2022 Practice Parameter Update, Journal of Allergy and Clinical Immunology, 2022, https://doi.org/10.1016/j.jaci.2022.08.028

• Penicillin is a class of antibiotics in a larger group known as beta-lactam antibiotics 
• It includes many specific antibiotics such as amoxicillin, penicillin G, ampicillin, piperacillin, nafcillin, and oxacillin 
• These antibiotics are commonly used to treat respiratory infections, urinary tract infections, sexually-transmitted infections, and ear or oral infections

• There is no evidence of a genetic inheritance for penicillin allergy 
• If a family member has a penicillin allergy, it does NOT mean you have one too, or that you are higher risk for one! 

• An allergy is a specific type of adverse reaction. It happens when your body's natural defense system learns to overreact to certain foreign substances that are normally safe 
• The result of that 'over-reaction' can be diverse, including making IgE antibodies specifically targeted towards an allergen. Most people react to allergens that they have been exposed to in the past
• IgE based allergic reactions are typically immediate in onset (within 1 hour), and often involve the skin with rashes or itching. 
  • In some cases, allergic reactions can result in anaphylaxis, which can be life-threatening. 
  • Rarely, people can have delayed drug reactions, these can involve multiple organs and can be dangerous 

• Non-allergic reactions are much more common than allergic reactions, and are often predictable based on the medication 
• In fact, allergic drug reactions only account for 5-10% of all adverse drug reactions
• For example, many antibiotics can irritate the intestines, causing gastrointestinal symptoms such as nausea, vomiting, or diarrhea. Those symptoms are most often not from an allergy!

• Over 90% of penicillin allergies have been found to be inaccurate 
• In addition, about 80% of penicillin allergies will disappear over 10 years 
• Inaccurately labelled penicillin allergies mean:
  • Doctors cannot give you the optimal antibiotics, and instead often have to rely on second-line drugs 
  • This increases the risk of creating bacterial superbugs and leads to worse outcomes for yourself. Inaccurate labels are associated with increased hospital stay, greater drug cost, and higher mortality in hospital
• De-labeling of inaccurate allergies can improve your personal health AND public health!

• Most commonly, penicillin allergy is first tested using skin testing. This is completed by an Allergy & Immunology specialist and has been validated for certain types of reactions. However, the gold standard is a drug challenge!
• For people with low risk of true penicillin allergy, proceeding directly to oral penicillin challenge has been shown to be a safe and reliable method of testing 
  • Oral challenge must be done under the supervision of a doctor, as a true allergy can result in an anaphylactic reaction requiring emergency care 
  • The challenge consists of consuming a standard dose of amoxicillin, followed by a period of observation to ensure there is no reaction  
  • For those that have a high risk of allergy but require penicillin, your doctor may refer you to a specialist for a process called desensitization (this is different from an oral challenge) 

• A negative test means that you have either lost the allergy over time or were not allergic to begin with! 
• You are safely able to take penicillin without increased risk of an allergic reaction
• This does not provide information on allergies to other medications 

• A positive test means that you are allergic to penicillin
• You should continue to avoid penicillin antibiotics 
• Make sure to keep a list of allergies and let your healthcare providers know about your allergies