Which antibiotic is contraindicated if a patient has a known allergy to penicillin?

The correct response highlights the principle of cross-reactivity in antibiotic allergies, particularly between penicillins and certain other classes of antibiotics. While aztreonam is a monobactam antibiotic and is generally considered safe for patients with a penicillin allergy due to its unique beta-lactam structure, it is important to note that in some rare cases, cross-reactivity can occur with those who have a severe penicillin allergy.

In contrast, ampicillin, cephalexin, and cefepime belong to classes closely related to penicillin, such as aminopenicillins and cephalosporins. These antibiotics may exhibit a higher likelihood of causing allergic reactions in patients with penicillin allergies, particularly those with a history of severe reactions.

This consideration is crucial in clinical practice when prescribing antibiotics, as it ensures patient safety and minimizes the risk of adverse reactions related to hypersensitivity. Therefore, while aztreonam is not absolutely contraindicated, caution should be exercised, especially in those with a history of severe penicillin allergy, making it important to be aware of the possibility of cross-reactivity in this specific patient population.