Benzylpenicillin skin testing is still important in diagnosing immediate hypersensitivity reactions to penicillins.

Background: The fact that both Hollister-Stier and Allergopharma ceased the production of penicilloyl-polylysine (PPL) and minor determinant mixture (MDM) in 2004 is severely hampering the diagnosis of beta-lactam hypersensitivity and may produce negative consequences.

Objective: To assess the contribution of skin testing with benzylpenicillin to the diagnosis of immunoglobulin E-mediated hypersensitivity to penicillins, in order to determine how much such testing could compensate for PPL and MDM unavailability.

Methods: We selected patients with histories of immediate reactions to penicillins and positive results to skin tests for one or more penicillin reagents (PPL, MDM, or benzylpenicillin), one or more semi-synthetic penicillins (ampicillin, amoxicillin, or piperacillin), or both.

Results: A total of 300 patients were selected, 105 in the French center and 195 in the Italian centers. Amoxicillin and ampicillin were the main responsible drugs. The most common clinical manifestation was anaphylaxis. The reagents most frequently positive to skin tests were amoxicillin (188, 62.7%), ampicillin (151, 50.3%), and benzylpenicillin (111, 37.0%). Among the 300 subjects, 113 (37.7%) were positive only to semi-synthetic penicillins, 109 (36.3%) to both semi-synthetic penicillins and the classic penicillin reagents, and 78 (26.0%) only to the latter. In the last group, 64 (21.3% of the 300 subjects) were positive only to PPL and/or MDM and 14 (4.7%) to benzylpenicillin, of whom 8 (2.7%) were positive only to the latter.

Conclusions: Skin testing with benzylpenicillin can partially compensate for PPL and MDM unavailability. Moreover, it can slightly increase the allergologic workup's sensitivity and therefore reduce the number of potentially dangerous challenges.