Background: In patients who were clinically diagnosed as having beta lactam allergy and had negative skin tests, the rates of reported resensitization to beta lactams after subsequent exposures, vary significantly. Some allergists advocate skin testing before every exposure to beta lactams.
Objective: We sought to determine the true rate of beta lactam allergy and of resensitization in children with a positive history for suspected beta lactam allergy.
Methods: The study was conducted from July 1998 to May 2004, with follow-up during 2007. Beta lactam allergy tests with the major determinant and freshly prepared minor determinant mixtures were offered to history positive children. Negative skin tests were followed by oral challenge. The tests were performed again 1-5 months later in order to address the possibility of resensitization.
Results: Tests were performed on 166 children: 150 for penicillins alone, 14 for penicillin in combination with cephalosporins, and an additional 2 patients solely for cephalosporins. Only 10 children (6%) were positive in the initial evaluation, four by skin test and six by oral challenge. A second set of tests was performed in 98 children with a negative initial evaluation; only two children (2%) were resensitized. On a follow-up survey of 71 of the 96 patients, 59 (83%) had received beta lactams; only one had developed a minor rash after subsequent exposure to amoxicillin.
Conclusions: Most children with suspected beta lactam allergy were not allergic to beta lactams. Resensitization to beta lactam antibiotics in children in this study was infrequent. In children with a clinical diagnosis of beta lactam allergy and negative skin tests, repeated skin testing before every exposure is usually unnecessary.