Allergy to penicillin is very commonly documented in patient charts, but is much less common than perceived by the general population. The reported prevalence of penicillin allergy is about 10%, however, more than 90% of patients are found not to be allergic. In patients found to have true penicillin allergy, the frequency of positive skin test results decreases over time. Clinical evaluation of these patients is important to help decease drug resistance, decrease healthcare costs and improve patient outcomes.

Appropriate evaluation of patients with a history of penicillin allergy can be accomplished by gathering historical information regarding reaction in addition to skin testing. Most drug reactions are either type I IgE-mediated reaction (immediate) or type IV (delayed) reaction. Immediate reactions generally occur within the first hour after initial dosing, but can take up to two hours particularly if medication was taken orally and with food. Symptoms can include hives, itching, swelling, wheezing, shortness of breath, low blood pressure and loss of consciousness. Delayed type responses generally occur days into treatment. Symptoms can include various skin reactions, anemias, kidney dysfunction, and other types of systemic illness. The most common reaction is a skin rash or hives. Positive response to epinephrine and antihistamines within a few hours of a reaction may indicate an immediate hypersensitivity reaction. Many skin reactions are a result of viral or bacterial infections. Also important to ascertain is whether a patient has tolerated other similar antibiotics (beta – lactams). This could indicate that the patient is not or no longer allergic to penicillin.

Even though skin testing can only identify a type I allergic response, it is this response that can lead to an anaphylactic reaction so it is important to be able to identify or rule out this type allergic issue. Risk factors for a hypersensitivity reaction include frequent or repeat courses of penicillin and high dose IV penicillin. Age and history of other allergic disease are not risk factors. Most patients lose allergic sensitivity to penicillin over time. Nearly 50% of patients are no longer allergic within 5 years of a reaction, and 80% or more by 10 years.

Penicillin allergy is the most commonly reported a drug allergy in the United States. Ninety percent of patients labeled as penicillin allergic are able to tolerate the drug. Adequate evaluation for true penicillin allergy with thorough history, skin testing and graded oral challenge can improve overall healthcare by decreasing cost and improving patient outcomes.
An Allergist-Immunologist is specialty trained in the diagnosis and treatment of allergic reactions, including penicillin allergies. If you would like to learn more about Penicillin allergy, contact your trusted Allergy Partners physician or visit allergypartners.com.

References:
Gonzalez-Estrada A, Radojicic C. Penicillin allergy: A practical guide for clinicians. Cleve Clin J Med. 2015 May:82(5):295-300
Nadarajah K, Green GR, Naglak M. Clinical outcomes of penicillin allergy testing. Ann Allergy Asthma immunol 2005;95:95:541-545.