A 57-year-old woman reports a history of hives, throat constriction, and bronchospasm within 30 minutes of receiving amoxicillin 10 years ago. She presented to the Emergency Department and required treatment with epinephrine. She now requires treatment with penicillin. She is evaluated by an allergy specialist who proceeds with outpatient penicillin skin testing for the major determinant (penicilloyl-polylysine [PPL/Pre-Pen]) and minor determinant (penicillin G), which are negative at the skin prick and intradermal levels.