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Penicillin Allergy – what do you need to know?

Penicillin AllergyPenicillins are widely used antibiotics that have important roles in treating bacterial infections. 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% will lose this tendency over a 10 year period. Consequently, although approximately 10% of the population is labeled as being allergic to penicillin, over 90% of these individuals actually are negative on allergy evaluation 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.

Symptoms of Penicillin Allergy and Treatment
Immediate allergic reactions to penicillins typically occur quickly (less than an hour) after receiving a dose of the medication, and often occur in patients who have tolerated previous courses of penicillin without issue. Symptoms frequently involve the skin and include:
•    Hives (also known as welts or urticaria, a raised, itchy rash)
•    Swelling (also known as angioedema, commonly occurs around the face and extremities such as hands and feet)

Treatment of these reactions usually involves an antihistamine and sometimes an oral or injected corticosteroid.
In rare cases, more serious reactions that suggest anaphylaxis can occur, including the following:
•    Swelling of the tongue, throat and lips
•    Respiratory symptoms such as difficulty breathing, coughing, chest tightness, wheezing
•    Light-headedness, loss of consciousness (caused by low blood pressure)

These symptoms require immediate treatment with epinephrine, which can be given with an autoinjector if available, and/or at the nearest emergency room or by calling Emergency Medical Services. Additional treatments may include albuterol to treat respiratory symptoms, IV fluids, and corticosteroids.

Penicillin Allergy Diagnosis
Penicillin allergy can be evaluated by an allergist / immunologist, 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. It typically takes about 2 to 3 hours to perform all of the testing.

In cases of a positive penicillin test, either the skin prick or intradermal test will produce a red, raised bump, signifying the presence of an allergy to the medication. Penicillins need to be avoided and a different antibiotic will be needed to treat infections. If a penicillin is needed, a desensitization procedure can be performed under the care of an allergist / immunologist to temporarily allow the drug to be used.

Find out more about drug allergies.

Penicillin Allergy FAQ

Check out our penicillin allergy infographic.

Visit our Penicillin Allergy Center.

The AAAAI's Find an Allergist / Immunologist service is a trusted resource to help you find a specialist close to home.

Importance of Penicillin Allergy Challenge
Learn more about why undergoing a Penicillin Allergy Challenge is important and how it is conducted in both adults and children.

Amoxicillin Challenge: Why Is It Important and How Is It Done?

Amoxicillin Challenge: Why Is It Important For My child and How Is It Done?

Learn more about how a challenge is done.

Episode 98: Everyone with Penicillin Allergy Warrants EvaluationRamsey

Drug allergy expert Allison Ramsey, MD, FAAAAI, discusses the importance of proactively delabeling patients with reported penicillin allergy. This is a must listen for all healthcare professionals…and relevant to at least 10% of the general population. (September 19, 2023)

Listen to the podcast.