Desensitization of anaphylactic hypersensitivity specific for the penicilloate minor determinant of penicillin and carbenicillin

A 68-yr-old man with a history of a morbilliform rash caused by intravenous penicillin required carbenicillin (CB) therapy for refractory Serratia marcescens septicemia. Skin testing showed a positive immediate skin test to the penicilloate minor determinant in the presence of negative tests to benzylpenicilloylpolylysine (BPL) and penicillin G (PG), as well as cross-reactivity between the penicilloate derivatives of PG and CB. True densensitization was accomplished by gradual administration of CB intravenously and was accompanied by a diffuse flush reaction. There was specific loss of wheal-and-flare reactivity as well as of specific serum reaginic antibody activity during the procedure, and there was no evidence of activation of serum complement. This case illustrates the usefulness of skin tests in the prediction and management of penicillin allergy and presents data pertaining to immunologic mechanisms involved in true desensitization.