5/5/2023 0 Comments Cephalosporin cross reactivity![]() ![]() There are no data of which I am aware of that shows that it is unsafe for individuals with confirmed or unconfirmed cephalexin allergy to use amoxicillin. “All of the data that I am aware of addresses the question of cephalosporin use in the setting of a penicillin “allergy”.Ĭephalexin “allergy” is a least an order of magnitude rarer than penicillin allergy. Eric Macy, an internationally recognized expert in penicillin and other antibiotic allergy. Ampicillin has a greater similarity with the R1 cephalexin side chain compared to amoxicillin, and amoxicillin is generally the antibiotic used (1). With the frequent occurrence of amoxicillin rash, which could be a side-chain sensitivity though many times it is related to a concomitant viral infection, I do not see problems specifically with cephalexin reactions, despite the similarity of the side chains. It seems that most of the reactivity of cephalosporins, certainly beyond the first generation, are to side chains, and fortunately side chain reactions tend to be less severe. I also am not aware of specific recommendations related to individuals with cephalosporin allergy with respect to treatment with a penicillin. ![]() Is that difference sufficient to render amoxicillin safe for the majority of cephalexin allergic patients? However, there is not a clear comment on the likelihood of safety of amoxicillin in cephalexin allergic patients, which also appears to have a fairly similar R group differing by only a hydroxyl substitution on the benzene ring. Zagursky and Pichichero have written two excellent articles on beta-lactam cross-reactivity and R group similarities between cephalexin and several penicillins including ampicillin, piperacillin, and several others that are much less common in the western US. However, the reverse guidance on which penicillins may be problematic in patients that have an allergy to cephalexin (one of our most commonly used first line cephalosporins) is much more difficult to find. There are a number of excellent papers in the literature that offer guidance for safe administration of second and higher generation cephalosporins to penicillin allergic patients. ![]()
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