To assess cross-reactivity between amoxicillin and cephalexin through the use of provocative oral challenges
As part of the LACTAAM (beta-lactam and other antibiotic registry) we conducted a graded oral challenge (GOC) to cephalexin in children who had established allergy to amoxicillin based on GOC at the Montreal Children’s Hospital. Children were monitored for immediate reactions (developing within one hour) and non-immediate reactions. Parents were instructed to contact the allergy clinic should a non-immediate reaction occur. Descriptive statistics were used.
Among 12 children with previous positive GOC for amoxicillin, 7 were males and the median age was 5.2 years. None of the previous reactions consisted of anaphylaxis. Half of cases had an immediate reaction to previous challenge to amoxicillin. Among 12 cephalexin-naïve children with a positive GOC to amoxicillin, an oral challenge to cephalexin was negative in all cases. There were no cases of non-immediate reaction (confirmed by telephone follow up 5-7 days post-challenge).
Due to structural similarities, cephalexin has been traditionally thought to elicit cross-reactivity in children allergic to amoxicillin. Despite confirmed amoxicillin allergy, the rate of allergy to cephalexin may be lower than once believed. Future large-scale studies are required to establish challenge proven data on cross-reactivity to cephalosporins in penicillin-allergic patients.