Penicillin Allergy

Medically Reviewed By William C. Lloyd III, MD, FACS
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What is penicillin allergy?

Penicillin allergy is an abnormal immune system response that occurs after taking the antibiotic penicillin, or another drug in the penicillin family. Allergy to penicillin can result in inflammation, swelling, hives, breathing difficulties, and even anaphylaxis (life-threatening allergic reaction). Symptoms of penicillin allergy occur due to your body’s immune response to the penicillin, which it mistakenly perceives as a danger or threat. In some cases, this response can be a severe, even life-threatening, reaction known as anaphylaxis, which includes airway constriction, low blood pressure (hypotension), and swelling of the throat or tongue.

Penicillin allergy is the most common cause of medication-related asthma in the United States. Approximately 3 to 10% of Americans have penicillin allergy. An estimated 10% of people who have penicillin allergy remain allergic their entire lives (Source: CDC).

The signs and symptoms of penicillin allergy can appear within a few minutes to several days after taking penicillin. Some people with penicillin allergy have mild symptoms, such as a skin rash, while others may have severe swelling of the throat or tightening in the lungs, causing difficulty breathing, which may be life threatening. Fortunately, you can prevent symptoms of penicillin allergy by following commonsense avoidance practices, such as asking whether your medications contain penicillin before you take them, making sure all health care providers know of your allergy, and wearing medical alert jewelry to preclude penicillin use should you need to receive emergency care.

Seek immediate medi cal care (call 911) for serious symptoms, such as sweating and severe difficulty breathing, difficulty swallowing, or sudden swelling of the throat, tongue or lips. Seek prompt medical care if you are being treated for penicillin allergy but mild symptoms recur or are persistent.

What are the symptoms of penicillin allergy?

Penicillin allergy causes inflammation that may result in a number of symptoms. The symptoms can vary in intensity from person to person. However, at any time, penicillin allergy may become severe or life threatening.

Symptoms of penicillin allergy

The symptoms of penicillin allergy are related to inflammation of the skin and respiratory system and include:

    Serious symptoms that might indicate a life-threatening condition

    In some cases, penicillin allergy can be life threatening. Seek immediate medical care (call 911) if you, or someone you are with, have any of these life-threatening symptoms including:

    What causes penicillin allergy?

    Penicillin allergy develops in people that have an immunoglobulin E (IgE)-mediated allergic reaction after taking penicillin. This type of allergic response includes swelling, rash or hives. If the reaction is severe, anaphylactic shock may result in airway constriction, low blood pressure (hypotension), and swelling of the throat or tongue.

    What are the risk factors for penicillin allergy?

    A number of factors increase the risk of developing penicillin allergy. Not all people with risk factors will get penicillin allergy. Risk factors for penicillin allergy include:

    • Age 20-49
    • Having a previous exposure to penicillin
    • Multiple drug allergies
    • Other allergic conditions, especially asthma
    • Receiving a penicillin drug in any form

    Reducing your risk of penicillin allergy

    You may be able to lower your risk of penicillin allergy by:

    • Asking what any medication is prior before you take it
    • Avoiding any medication with penicillin
    • Knowing what medications contain penicillin
    • Wearing a medical alert item that identifies a penicillin allergy

    How is penicillin allergy treated?

    Treatment for penicillin allergy reaction begins with seeking medical care from your health care provider. To determine whether you have penicillin allergy, you will be asked questions about your symptoms and when they occur.

    The mainstay of treatment for mild to moderate penicillin allergy reaction is antihistamine medications to reduce symptoms related to inflammation of the skin, such as hives, swelling, itching or rash. Respiratory symptoms, such as breathing difficulty and wheezing, are treated with bronchodilators. Corticosteroids may be administered to reduce inflammation either of the skin or airways. For severe penicillin allergy responses that include anaphylaxis, epinephrine is given subcutaneously or intramuscularly.

    In some cases, penicillin therapy may be the only effective medication to treat an infection. People in this situation who are penicillin allergic may undergo desensitization to reduce serious allergic reactions. This procedure should be done in a hospital using oral or IV preparations. Once the person has been desensitized, he or she may be given penicillin. It is important to complete the entire regimen of penicillin therapy to avoid reinfection.

    What are the potential complications of penicillin allergy?

    Complications of untreated penicillin allergy can be serious, even life threatening in some cases. You can help minimize your risk of serious complications by following the treatment plan you and your health care professional design specifically for you. Complications of penicillin allergy include:

    • Anaphylaxis (life-threatening allergic reaction)
    • Angioedema (severe swelling under the skin)
    • Shock
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    Medical Reviewer: William C. Lloyd III, MD, FACS
    Last Review Date: 2021 Jan 18
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    THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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    2. Drug allergies. Medline Plus, a service of the National Library of Medicine National Institutes of Health.
    3. Joint Task Force on Practice Parameters, American Academy of Allergy, Asthma and Immunology, American College of Allergy, Asthma and Immunology, Joint Council of Allergy, Asthma and Immunology. Drug allergy: an updated practice parameter. Ann Allergy Asthma Immunol 2010; 105:259.