Cephalosporins Often Safe in PCN-Allergic Patients

Bottom line The risk of cross-reactivity between penicillin and cephalosporins has been overestimated for second- and third-generation drugs. It is only a significant risk in first-generation cephalosporins that have a similar side chain to penicillin (cephalothin, cephalexin, cefadroxil, and cefazolin). With appropriate monitoring physicians could consider using second- and third-generation cephalosporins in these patients. (LOE = 2a)

Synopsis The author did a comprehensive search of MEDLINE and EMBASE to identify the 101 articles that were used as the basis for this systematic review. The overall rate of rash is approximately 2%. Anaphylaxis is very rare, with a risk between 0.1% and 0.0001%. Physicians often worry about cross-reactivity between penicillins and cephalosporins, but this only seems to apply to first-generation cephalosporins such as cephalothin, cephaloridine, cephalexin, cefadroxil, or cefazolin. No increase in the risk of an allergic reaction is seen in second- and third-generation cephalosporins, including cefprozil, cefuroxime, ceftazidime, cefpodoxime, and ceftriaxone. The author speculates that this is because of similar side chains in the chemical structure between penicillins and first-generation (but not second- or third-generation) cephalosporins. Patients with a previous IgE mediated reaction to penicillin (eg, wheezing, angioedema, urticaria, laryngeal edema, or anaphylaxis) should not use first-generation cephalosporins but may be able to safely take second- and third-generation cephalosporins

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