Background: Studies suggest that 90% of patients labelled as allergic to penicillin tolerate it
after rigorous assessment. Here, we examined the true frequency of allergies to beta-lactam
antibiotics subclasses, as well as the negative predictive value (NPV) of skin testing in an adult
population referred to a university allergy clinic in Switzerland.
Methods: This is a retrospective study in which we examined the clinical records of patients
who were investigated for a label of allergy to beta-lactam (penicillin, cephalosporin or
carbapenem) antibiotics between January 1st 2011 and December 31st 2018.
Results: 582 patients were identified with a documented allergy to beta-lactam antibiotics
and 477 patients were systemically investigated by skin tests and/or drug challenge to confirm
or rule out allergy. 262 patients reported a history of immediate reactions, 137 of delayed
reactions, and 114 of unknown reactions. Overall, 88 (15.1%) patients were truly allergic to
any beta-lactam antibiotics; 64 (11.0%) with an immediate reaction and 24 (4.1%) with a
delayed reaction. Most frequently identified true allergy was penicillin (65 patients), followed
by cephalosporin (21 patients) and carbapenem (2 patients). NPV of skin tests for all beta-
lactam were 97.7% and 92.5% for immediate and delayed reactions, respectively, and 96.3%
and 92.1% when penicillin was considered. Systemic allergic reaction occurred in 0.6% of skin
tests and in 3.1% of drug challenges.
Conclusions: Only 15.1% of patients with beta-lactam allergy label are truly allergic and non-
allergic patients can be safely identified and delabelled by a rigorous allergic work-up based
on skin tests and drug challenge.