What is the risk of using a cephalosporin in a patient with a penicillin allergy?

Abstract

suggested that the absolute risk of an allergic reaction to cephalosporins in an individual allergy to penicillin is actually very low and the risk of severe consequences of an allergic reaction is even lower. Anaphylaxis occurred in less than 0.001% of patients taking a cephalosporin who had a previous history of a penicillin allergy. This same study by Apter et al (5) also demonstrated that the relative risk of a reaction in a patient with a penicillin allergy, who subsequently takes a cephalosporin, is increased compared with individuals who received cephalosporin with no prior history of a penicillin allergy (unadjusted RR = 10.0; CI 7.4 to 13.6), with 1.1% of patients having events after both penicillin and cephalosporin. However, there was a similarly increased risk when the penicillin-allergic patient was given a sulfonamide as the second medication when compared with those who received sulfonamide without a history of penicillin allergy (unadjusted RR = 7.2; CI 3.8 to 13.5), with 1.6% of patients having events after both penicillin and sulfonamide. As a result, Apter et al (5) concluded that cross-reactivity could not fully explain these results, and because the risk of very severe reactions in their study was low, they believed that cephalosporins could be considered for treatment of patients with a penicillin allergy. There is also evidence to support that certain cephalosporins are more likely than others to cross-react with penicillin. Atanaskovic-Markovic et al (4) demonstrated that cross-reactivity between cephalosporins and penicillins depends on the generation of cephalosporins with cross-reactivity being higher with earlier generation of cephalosporins, and varying between 0.3% and 23.9%. Pichichero (1), in a recent review of the evidence, stated that because the degradation process of the beta-lactam rings is different for penicillins than it is for cephalosporins, the similarity in structure of the beta-lactam rings as a predictor of cross-reactivity may be less important than once thought. Pichichero also cited that evidence is growing to support the idea that a cephalosporin’s ability to generate an immune response is linked to the chemical structure of its side chain. He concluded that medications with similarly structured side chains may be more likely to cross-react than