Background and Objective: Administration of carbapenems to β-lactam-allergic patients has always been considered potentially harmful
because of a 47.4% rate of cross-reactivity to imipenem reported in a single study. Nevertheless, recent studies have shown that the rate
of cross-reactivity of imipenem and meropenem with penicillins is lower than 1%. The aim of this study was to evaluate the possibility of
using ertapenem in patients with an established IgE-mediated β-lactam allergy.
Patients and Methods: We studied all participants who came to our allergy unit and had a clinical history of immediate hypersensitivity
reactions to β-lactams. The inclusion criteria were a positive skin test result to at least 1 β-lactam molecule and/or positive specific IgE
(when available). All participants underwent immediate-type skin tests with several β-lactam molecules including ertapenem. Challenges
with intravenous ertapenem were performed on 2 different days in patients with negative skin test results.
Results: We examined 49 patients with a clinical history of immediate reactions to β-lactams. All the patients had positive skin tests
and/or positive specific IgE to at least 1 β-lactam reagent and negative carbapenem skin tests. Thirty-six patients agreed to undergo the
challenges and 35 tolerated the full dose of ertapenem.
Conclusions: The practice of avoiding carbapenems in patients with β-lactam allergy should be abandoned considering the very low rate
of cross-reactivity. β-Lactam-allergic patients who need ertapenem therapy should undergo skin tests and, if negative, a graded challenge
to assess tolerability.
Key words: β-lactams. IgE-mediated hypersensitivity. Ertapenem. Cross-reactivity.