Background: Skin testing with major and minor determinants of benzylpenicillin is recommended standard practice for the evaluation of patients with immediate hypersensitivity reactions to β-lactams. However, commercial reagents for this purpose were recently dropped from the European market.

Objective: In the present study, we assessed a new brand of reagents for use in skin testing in patients with suspected penicillin allergy.

Methods: Prick tests and intradermal tests were performed with benzylpenicilloyl polylysine (PPL) and minor determinant mixture (MDM). Penicillin G, amoxicillin, and the culprit β-lactam were also tested. If skin tests were negative, a single-blind oral challenge test was performed with the culprit active principle or penicillin. If both skin tests and challenge tests were negative, the same procedure was repeated between 2 and 4 weeks later.

Results: A total of 636 patients were assessed. The allergy study was positive in 69 patients. Skin tests with PPL were positive in 30 patients (46.8%) and with MDM in 28 (43.7%). Sixteen patients displayed a positive reaction to both PPL and MDM (25%), while 42 patients (65.6%) had a positive reaction to either PPL or MDM alone. Thirty-two patients had positive skin test reactions to penicillin G or another β-lactam antibiotic. Five patients in whom a negative result was obtained in skin tests had a positive reaction to oral challenge.

Conclusions: Our results indicate that a new brand of determinants that is commercially available in Europe is a reliable and useful tool for the diagnosis of β-lactam allergy. The new reagents are a safe alternative to the previously available brand.

Key words: Penicillin allergy. Drug allergy. Major determinants. Minor determinant mixture. Benzylpenicilloyl polylysine.