If a client has a penicillin allergy, which other antibiotic may they also react to?

A client with a penicillin allergy may also react to cephalosporins because of the structural similarities between penicillin and certain cephalosporins. Both classes of antibiotics belong to the beta-lactam family, which means they share a similar chemical structure that can provoke an immune response in individuals with a history of penicillin allergies.

This cross-reactivity occurs because the immune system may recognize the shared beta-lactam ring as a similar antigen, leading to allergic reactions. Although not all cephalosporins will cause reactions in patients with penicillin allergies, the potential for cross-reactivity, especially with first-generation cephalosporins, is significant enough to warrant caution.

In contrast, macrolides, aminoglycosides, and tetracyclines have distinct chemical structures and mechanisms of action that do not share the beta-lactam ring, therefore they are less likely to provoke an allergic reaction in a patient with a penicillin allergy.