Natural evolution of skin test sensitivity in patients allergic to beta-lactam antibiotics

Background: Subjects with immediate reactions to penicillins and positive s kin test responses may lose sensitivity if penicillin is avoided. The longe r the interval between the reaction and the skin test, the greater the like lihood of having a negative result. Objective: We sought to study prospectively the evolution of skin test sens itivity in a group of subjects allergic to penicillin with positive skin te st responses to different penicillin determinants. Methods: Skin tests were performed with major and minor determinants of ben zylpenicillin (BPO/MDM), amoxicillin (AX), and ampicillin-at the initial ev aluation and repeated 1, 3, and 5 years later if the responses were still p ositive. Subjects were divided into 2 groups. Group A consisted of patients with a positive skin test response to benzylpenicilloyl or minor determina nt mixture, and group B consisted of those with a selective response to amo xicillin and good tolerance to benzylpenicillin. Results: In group A (n = 31) after 1 year, 25 patients continued to have po sitive responses and 6 began to have negative responses; after 3 years, 18 continued to have positive responses, 5 began to have negative responses, a nd;2 were lost to follow-up; and after 5 years, 12 continued to have positi ve 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 resp onses after 1 year; 6 had positive: responses, 5 had negative responses, an d 1 was lost to followup after 3 years; and no patients had positive respon ses, 5 had negative responses, and 1 was lost to follow-up after 5 years. S urvival analysis showed significant differences between groups (log-rank te st = 12.8; P < .0003). Conclusion: Patients with a selective response to amoxicillin tended to los e sensitivity faster than those who responded to several penicillin determi nants, supporting the existence of at least 2 distinct types of IgE respons e in patients allergic to beta-lactam.