Background: Delayed reactions with betalactam antibiotics are a very common reason for consultation and a matter of numerous publications.
Objective: To demonstrate that delayed reactions occurring during treatment with betalactam antibiotics are not reproduced in a high percentage of the patients, when making drug challenge. To analyse the characteristics of people showing this type of reaction.
Methods: We included in our study all the patients who came to our Allergy Department during one year (2004), with a clinical history of delayed reaction (> 72h) to betalactams. Skin prick tests (SPT), intradermal tests (IT) and patch tests were carried out, followed by simple blind placebo controlled drug challenge (SBPCDC) at hospital and home treatment with betalactams.
Results: We studied 23 patients (12 men and 11 women), average age 23.4 years old. SPT and patch test were negative in all patients. Only one patient showed positive IT tests, and allergic reaction was only reproduced in two patients; 76 % tolerated the drug involved in supposed allergy.
Conclusions: Simple blind oral challenge with implicated drug followed by home treatment is required for a conclusive diagnosis of allergy in patients with delayed reactions to betalactams.