Background: Subjects with immediate reactions to penicillins and positive skin test responses may lose sensitivity if penicillin is avoided. The longer the interval between the reaction and the skin test, the greater the likelihood of having a negative result.
Objective: We sought to study prospectively the evolution of skin test sensitivity in a group of subjects allergic to penicillin with positive skin test responses to different penicillin determinants.
Methods: Skin tests were performed with major and minor determinants of benzylpenicillin (BPO/MDM), amoxicillin (AX), and ampicillin at the initial evaluation and repeated 1, 3, and 5 years later if the responses were still positive. Subjects were divided into 2 groups. Group A consisted of patients with a positive skin test response to benzylpenicilloyl or minor determinant mixture, and group B consisted of those with a selective response to amoxicillin and good tolerance to benzylpenicillin.
Results: In group A (n = 31) after 1 year, 25 patients continued to have positive responses and 6 began to have negative responses; after 3 years, 18 continued to have positive responses, 5 began to have negative responses, and 2 were lost to follow-up; and after 5 years, 12 continued to have positive responses, 5 began to have negative responses, and 1 was lost to follow-up. In group B (n = 24) 12 had positive responses, and 12 had negative responses after 1 year; 6 had positive responses, 5 had negative responses, and 1 was lost to follow-up after 3 years; and no patients had positive responses, 5 had negative responses, and 1 was lost to follow-up after 5 years. Survival analysis showed significant differences between groups (log-rank test = 12.8; P <. 0003).
Conclusion: Patients with a selective response to amoxicillin tended to lose sensitivity faster than those who responded to several penicillin determinants, supporting the existence of at least 2 distinct types of IgE response in patients allergic to beta-lactam.