Penicillin allergy is reported by up to 10 percent of people. A common clinical question is whether these individuals can safely receive structurally-related antibiotics, such as cephalosporins, carbapenems, and monobactams.
This topic will discuss cross-reactivity between penicillins and structurally-related antibiotics in patients with type I, immunoglobulin E (IgE)-mediated allergy to penicillins. Penicillin allergy, skin testing, graded challenge (test dosing), and desensitization are reviewed separately. (See "Allergy to penicillins" and "Penicillin skin testing".)
Antigenic components of penicillins — In order to understand the possible cross-reactivity among penicillins, cephalosporins, carbapenems, and monobactams, it is helpful to review the potential allergens in penicillins. Patients with IgE-mediated allergy to penicillins may be reactive to the beta-lactam ring structure that is common to all penicillins, or to the R group side chains that distinguish different penicillins from one another. In the United States, most penicillin-allergic patients are sensitive to the beta-lactam core. In contrast, in southern Europe where amoxicillin constitutes 90 percent of antibiotic use in some European countries, up to one-third of patients are said to react to the R group side chain. (See "Allergy to penicillins", section on 'Side-chain specific reactions'.)
●A beta-lactam structure is also found in cephalosporins, carbapenems, and monobactams (figure 1).
●The aminopenicillins amoxicillin and ampicillin each have R group side chains that are identical to the side chains of certain cephalosporins (table 1).