Penicillin Allergy Testing

Penicillins are commonly prescribed antibiotics that treat bacterial infections. Penicillin allergies are rare but can occur. The allergy to penicillin occurs when the immune system becomes hypersensitive to the penicillin and mistakes the drug for a harmful substance. In response to penicillin, the body releases chemicals to fight the antibiotic, causing an allergic reaction.

Penicillin allergies can appear in patients who have tolerated penicillin class antibiotics in the past. However, some side effects of penicillin – as happens with other medications – can occur that are not due to an allergic reaction to the drug, such as mild nausea or headaches. Since penicillin class antibiotics are safe and effective, it is important to know whether an individual really has an allergy to penicillin, so that they can receive the most appropriate care. At Skin and Laser Dermatology Center, individuals with a history of allergies, a suspicion they may have a penicillin allergy, or those who actively have such an allergy can be evaluated by a board-certified allergist and immunologist. This allows patients to have the best information and ease of mind when considering their potential for a penicillin allergy.

How common are penicillin allergies?

According to the Center of Disease Control (CDC), approximately 10% of all U.S. patients have reported an allergic reaction to a penicillin class antibiotic in their past. However, when evaluated, less than 1% of the population is truly allergic to penicillins.

What symptoms are characteristic of a penicillin allergy?

Immediate allergic reactions to penicillins typically occur less than an hour after receiving the medication. Less commonly, reactions can occur hours, days, or weeks later. There are many symptoms possible during a penicillin allergic reaction, but some of the common ones are:

• Hives, a raised, itchy rash (urticaria)
• Wheezing and shortness of breath
• Itchy, watery eyes
• Swelling, often on the face and extremities (angioedema)

Anaphylaxis, a rare, life-threatening allergic reaction which affects multiple systems in the body and requires immediate medical attention.

How is an allergic reaction to penicillin treated?

An allergic reaction to penicillin will often be treated with an antihistamine and sometimes an oral or injected corticosteroid, depending on the symptoms and severity of the case. For some patients, additional treatments may be needed to treat respiratory symptoms. If anaphylaxis occurs, immediate treatment with epinephrine should be administered.

How is a penicillin allergy tested for?

Based on a patient’s history and physical exam, a penicillin skin test may be conducted by a board-certified allergist and immunologist to confirm a penicillin allergy. Penicillin skin tests are reliable ways to evaluate for a penicillin allergy. If the penicillin skin test is positive, the patient likely has a penicillin allergy. If a patient does not show a reaction to penicillin with a skin test, oral penicillin may be delivered to safely rule out a penicillin allergy.