A diagnostic protocol for evaluating nonimmediate reactions to aminopenicillins

Background: Maculopapular and urticarial rashes are nonimmediate manifestations common during aminopenicillin (AP) treatment, and the former often represent cell-mediated hypersensitivity. Objectives: We sought to determine the significance and incidence of skin test reactions to APs in adults reporting adverse reactions during therapy with these beta-lactams and, particularly, to evaluate the potential of patch tests, delayed-reading skin tests, and challenges in the diagnosis of nonimmediate reactions. Methods: We used skin tests with penicilloylpolylysine, minor determinant mixture, benzylpenicillin, ampicillin, and amoxicillin, as well as patch tests with the last 3 drugs, We also performed in vitro assays for specific IgE and challenges with the suspect penicillin in subjects with nonimmediate reactions. Results: Among the 144 patients reporting nonimmediate manifestations (mostly maculopapular rashes), delayed hypersensitivity was diagnosed in 62 on the basis of positive patch test and/or delayed intradermal test results and responses to challenges; negative reactions to challenges allowed us to reasonably exclude the possibility of allergy in 66 subjects, and the challenge confirmed that 1 patient had linear IgA bullous dermatosis. Definitive diagnoses could not be provided for the remaining 15 subjects, who had negative allergologic test results, because they did not consent to challenges. In 40 of 49 immediate reactors, a diagnosis of IgE-mediated hypersensitivity was made. Conclusions: Both patch and intradermal tests are useful in evaluating nonimmediate reactions to APs. Positive patch test and delayed intradermal responses together indicate delayed hypersensitivity. Intradermal testing appears to be more sensitive than patch testing, but the pattern of positive delayed intradermal test responses and negative patch test responses needs further investigation because of false-positive cases.