The very limited usefulness of skin testing with penicilloyl‐polylysine and the minor determinant mixture in evaluating nonimmediate reactions to penicillins

BACKGROUND: The contribution of skin testing with penicilloyl-polylysine (PPL) and the minor determinant mixture (MDM) to the diagnosis of hypersensitivity reactions to penicillins differs greatly according to the type of reaction: immediate (occurring within 1 h after the last drug administration) or nonimmediate (occurring more than 1 h after the last drug administration). OBJECTIVE: To assess the contribution of skin testing with PPL and MDM to the diagnosis of nonimmediate reactions to penicillins. METHODS: We evaluated 162 adults who had had 232 nonimmediate reactions to penicillins, mostly aminopenicillins, and presented positive skin and/or patch tests to one or more penicillin reagents: PPL, MDM, benzylpenicillin, ampicillin, and amoxicillin, as well as any responsible penicillins. RESULTS: A total of 157 subjects (96.9%) displayed patch-test and/or delayed-reading intradermal-test positivity to penicillin reagents, which indicates a cell-mediated hypersensitivity; six of them also presented immediate-reading skin-test positivities. All 157 patients with a cell-mediated hypersensitivity were positive to the responsible penicillins (parent drugs); 16 of them also displayed delayed-reading intradermal-test positivity to MDM. Five (3.1%) of the 162 patients displayed only immediate-reading skin-test positivity (four to PPL and one to amoxicillin). Overall, 158 subjects (97.5%) presented positive responses to the responsible penicillins, while only 9 (5.5%) and 17 (10.5%) were positive to PPL and MDM, respectively. CONCLUSIONS: The contribution of skin testing with PPL and MDM in diagnosing nonimmediate hypersensitivity reactions to penicillins, especially cell-mediated ones, is very limited. This finding could be useful at a time when PPL and MDM are not available in all countries.