Cephalosporins and Penicillin Allergy

Are Cephalosporins Safe if You're Allergic to Penicillin?

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Can I Take Cephalosporins if I’m Allergic to Penicillin?

A common question that patients ask is if they can take a cephalosporin antibiotic if they are allergic to penicillin. These two types of antibiotics are similar -- and could be considered as "cousins" of each other. There is concern that if a person is allergic to cephalosporins, then they could be allergic to penicillins as well -- or vice versa.

Penicillin is perhaps the most well-known member of a group of antibiotics called beta-lactams, which refers to a particular structure in their chemical makeup. The structure is also shared by semi-synthetic penicillin (amoxicillin), cephalosporins, and other antibiotics (such as imipenem). Penicillins and cephalosporins are the most commonly used antibiotics to treat common infections.

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 varies 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.

Learn more about the diagnosis and treatment of penicillin allergy.


Perez-Inestrosa E, Suau R, Montañez MI, et al. Cephalosporin chemical reactivity and its immunological implications. Curr Opin Allergy Clin Immunol. 2005 Aug;5(4):323-30.

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.

Pichichero ME, Casey JR. Safe use of selected cephalosporins in penicillin-allergic patients: a meta-analysis. Otolaryngol Head Neck Surg. 2007 Mar;136(3):340-7.

Apter AJ, Kinman JL, Bilker WB, et al. Is there cross-reactivity between penicillins and cephalosporins? Am J Med. 2006 Apr;119(4):354.e11-9.

Annè S, Reisman RE. Risk of administering cephalosporin antibiotics to patients with histories of penicillin allergy. Ann Allergy Asthma Immunol. 1995 Feb;74(2):167-70.

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