[Penicillin allergy].

Betalactams are the most widely used antimicrobials for their safety and efficacy. These include the penicillins, cephalosporins, carbapenems, and monobactams. Penicillin allergy ranks first in relation to drug allergy. 10 to 20 % of the population is labeled as allergic to it, often wrongly. Cross reaction is reported in 2 to 5 % between penicillins and cephalosporin. There is no cross reaction between penicillins and aztreonam, but there is with ceftazidime. All the mechanisms of the Gell and Coombs classification are included in the pathophysiology of hypersensitivity reactions to penicillin. Stratification according to risk allows us to take the most objective behavior to label the patient as allergic to. In the natural history of penicillin allergy, 80-90 % of patients lose this sensitivity by 10 years. If necessary, the patient can undergo a desensitization protocol. The immuno-allergist is a key piece in the selection of the patient, the elaboration of the challenge and desensitization protocols, in a controlled environment.