Penicillins and cephalosporins are also the most common causes of drug allergy. About 10% of all Americans report an allergy to penicillin or a related antibiotic. Since penicillins and cephalosporins are related structurally, people with a history of penicillin allergy are often not given cephalosporins for concern that these will also cause an allergic reaction. This limits the available choices of antibiotics for people with penicillin allergy, and could possibly result in the delayed administration of antibiotics when a person has an infection.
Many studies have looked at the tolerability of cephalosporins in people with penicillin allergy. Nearly all of these studies show a low risk of reactions to cephalosporins in people with penicillin allergy, especially in terms of anaphylaxis. The exception appears to be to the first-generation cephalosporins, such as cephalexin (Keflex) and cefazolin (Ancef), which show higher rates of allergic reactions in people with penicillin allergy. Second- and third-generation cephalosporins, such as cefuroxime (Ceftin), cefprozil (Cefzil), cefdinir (Omnicef), and cefpodoxime (Vantin), do not appear to cause more allergic reactions in people with penicillin allergy.
Cephalosporins do cause allergic reactions independent of penicillin similarities, however. These reactions are often due to the structure of the cephalosporin side chain, which various from type to type of cephalosporin.
Therefore, while most people with a history of a penicillin allergy can tolerate cephalosporins, most allergists, including myself, use caution when giving a cephalosporin to a person with a history of penicillin allergy. Obviously, there are many factors involved in this decision, including the severity and type of the penicillin reaction, type of infection that needs to be treated, and appropriateness/availability of non-penicillin/non-cephalosporin antibiotics that could also be used. In my opinion, an oral challenge to a cephalosporin, under medical supervision, seems appropriate when giving a cephalosporin to a person with a penicillin allergy.
Learn more about the diagnosis and treatment of penicillin allergy.
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DePestel DD, Benninger MS, Danziger L, et al. Cephalosporin use in treatment of patients with penicillin allergies. J Am Pharm Assoc (2003). 2008 Jul-Aug;48(4):530-40.
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