Penicillin allergy is the most commonly reported drug allergy in the United States with roughly 10% of the general population reporting a penicillin allergy. Of the adult U.S. population, 3-10% has experienced an IgE-mediated allergic response to penicillin such as urticarial, angioedema, or anaphylaxis (upper airway obstruction, bronchospasm, or hypotension).
According to published research, without testing, an unverified history of penicillin allergy can contribute to longer hospitalizations, higher costs, greater risk for adverse effects of alternative (non-beta-lactam) antibiotics, and increased rates of serious antibiotic resistant infections such as C. difficile and methicillin-resistant Staphylococcus aureus (MRSA). Penicillin allergy testing is safe, effective and can even be performed even in critically ill patients or pregnant women.
Although the prevalence of life-threatening anaphylactic reactions to penicillin has been estimated to be between 0.02% and 0.04%, the most common reaction is a cutaneous eruption or hives. However, after undergoing a complete evaluation by a board-certified allergist, >90% of patients labeled as “penicillin-allergic” are able to tolerate penicillin without adverse reactions.
In patients found to have penicillin allergy, the frequency of positive results on skin testing decreases by 10% per year of avoidance. This suggests that 80-100% of patients are expected to test negative to penicillin allergy 10 years after their reaction.
Ruling out an IgE-mediated (severe, anaphylactic) reaction to penicillin can be beneficial to primary care providers, patients, and hospitals, allowing providers to prescribe cost-effective penicillin, thus decreasing the need for broad-spectrum antibiotics, and reducing healthcare costs to the patient and hospital.
What can I expect when seeing an allergist for evaluation?
The clinician will take a thorough history to distinguish whether the reaction is consistent with IgE-mediated or non-IgE-mediated reactions. Often, patients do not recall history of reaction or treatment course after reaction and penicillin remains on the allergy list.
The only validated test for diagnosing IgE-mediated reactions caused by penicillin is the immediate hypersensitivity skin test, which should be performed by a board certified allergist. Testing should be performed in a monitored setting in which treatment for an anaphylactic reaction is available and patients should not have taken antihistamines for 4-5 days. The test consists of skin-prick and intradermal testing with the major determinant (penicilloyl-polylysine; Pre-Pen), the minor determinant (penicillin G), a negative control (saline) and a positive control (histamine).
If skin testing is negative, the physician will administer a monitored dose challenge and monitor the patient in the office. If tolerated without reaction, penicillin may be removed from the allergy list and used as indicated in the future.
If skin testing is positive, the patient is advised to continue to avoid penicillin and use other antibiotics that are equally efficacious or undergo penicillin desensitization. During desensitization, patients receive progressively higher doses of the drug every 15-30 minutes (subcutaneously, intravenously, or orally) until a full therapeutic dose is achieved. This induces “a state of tolerance” to the drug and the penicillin must be continued daily. If the medication is stopped for >48 hours, the patient must undergo subsequent desensitization.
Patients with a history of penicillin allergy should visit their local Allergy Partners physician for evaluation which can help rule out life-threatening penicillin allergy, rectify Drug Allergy Lists and allow for more convenient, cost-effective treatment.
Dr. Timothy Campbell
Allergy Partners of Hampton Roads