Cross-reactivity between penicillins and ALL 3rd and 4th generation cephalosporins is negligible.Cross-reactivity between penicillins and MOST 1st and 2nd generation cephalosporins is negligible.The true incidence of an allergy to penicillin in patients believed to have such allergy is Overall cross-reactivity rate in patients with a confirmed penicillin allergy = 2.5%.Overall cross-reactivity rate between cephalosporins and penicillins in patients reporting a penicillin allergy = 1%.2nd generation cephalosporins: cefaclor, cefprozilĪ new review article of 27 articles on this very topic just came out reporting:.1st generation cephalosporins: cefadroxil, cefatrizine, cephalexin, cephradine.Such is the case with amoxicillin or ampicillin with: Therefore it makes sense that if a penicillin and a cephalosporin share that particular (R-1) side-chain similarity, the risk of cross-reactivity is increased. More recent studies have determined that the actual risk of cross-reactivity relates more to a side chain similarity and probably not the beta-lactam ring at all. The belief was that the beta-lactam ring similarities must be the cause. It turns out that prior to 1980, penicillins and cephaloporins were often produced using the same fungus and the chance for contamination during the manufacturing process was high. Well, I guess that means it’s fact, right? Not so fast!īackground: Cephalosporin-Penicillin Cross-Reactivity They probably said something about the risk being less with 3rd and 4th generations cephalosporins, but lets be honest… who remembers anything but that magic 10%? When I started working more with physicians, I found that they also learned the same 10% rule in medical school. I remember back to my days in pharmacy school when I learned that there was approximately a 10% risk of cross-reactivity, if a cephalosporin was given to a penicillin-allergic patient. To give or not to give a cephalosporin in penicillin-allergic patients?
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