"In cases of nonimmediate reactions (i.e., occurring more than one hour after the drug administration), it is mandatory to test the suspected penicillin (e.g., amoxicillin, ampicillin, etc.)."
All but 4 patients (97.5%) had positive responses to the responsible penicillins. Only 5.5% were positive to PPL (all immediate-reading) and only 10.5% were positive to MDM.
Hypersensitivity reactions to beta-lactam antibiotics: MAUS mnemonic 20-20-40-20%. Click here to enlarge the image.
Mnemonics for penicillin allergy skin testing
Major penicillin determinant test detects
Majority of patients with penicillin allergy
Minor determinant test
Minorizes the risk
Image source: Penicillin nucleus, Wikipedia, GNU Free Documentation License.