Is there cross-reactivity between penicillins and cephalosporins?
GROUND: We sought to determine the risk of an allergic reaction to a cephalosporin exposure in those with prior penicillin reactions. METHODS: We conducted a retrospective cohort study using the United Kingdom General Practice Research Database. We selected all patients receiving a prescription for penicillin followed by a prescription for a cephalosporin and identified allergic-like events within 30 days after each prescription. Allergic events were defined by 2 sets of codes: 1 more restrictive, 1 more inclusive. Comparison was made with a population of patients receiving a prescription for a penicillin followed by a prescription for a sulfonamide antibiotic. RESULTS: A total of 3,375,162 patients received a penicillin; 506,679 (15%) received a subsequent cephalosporin. Among patients receiving a penicillin followed by a cephalosporin, the unadjusted risk ratio of an allergic-like event for those who had a prior event, compared with those who had no such prior event, narrowly defined
