Penicillin skin testing accurately rules out penicillin allergy

Published online: March 13, 2019

Ten percent of the population claims an allergy to penicillin, but 90% or more of these individuals are not allergic. Patients labeled as penicillin-allergic have higher medical costs, longer hospital stays, are more likely to be treated with broad-spectrum antibiotics and develop drug-resistant bacterial infections. Penicillin skin testing is underutilized, one reason being that most penicillin skin test reagents are not Food and Drug Administration (FDA) approved or readily available to evaluate patients labelled penicillin-allergic.

In a recently published article in The Journal of Allergy and Clinical Immunology: In Practice, Solensky and colleagues determined the negative predictive value (NPV) of the Penicillin Skin Test Kit containing the major allergenic determinant (penicilloyl-polylysine), a minor determinant mixture (penicillin G, penicilloate, penilloate), and amoxicillin, produced according to FDA standards. The study was performed at 13 allergy centers in the United States. Adult subjects with a convincing history of penicillin allergy underwent penicillin skin testing using the Penicillin Skin Test Kit. Those who were skin test-negative underwent challenge with oral amoxicillin, whereas skin test-positive patients were not challenged. The NPV was defined as the percentage of subjects with negative skin tests who did not experience an allergic reaction following challenge.

In total, 455 patients with a history of penicillin allergy underwent skin testing and 63 (13.8%) had one or more positive tests; 65% of the positive tests were to the minor determinant mixture and/or amoxicillin alone. Of 373 skin test-negative subjects, 8 developed potential allergic reactions following oral amoxicillin challenge, translating to NPV of 97.9% (95.8, 99.1, 95% CI; p<0.0001). All but one of the reactions was mild or moderate, and most subjects who required treatment received only antihistamines.

The Penicillin Skin Test Kit, containing all relevant penicillin allergenic determinants, demonstrated very high NPV. Removal of a penicillin allergy label in a large majority of currently mislabeled patients has substantial personal and public health implications. The Penicillin Skin Test Kit is undergoing FDA review and will hopefully become commercially available in the near future.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.