Which antimicrobial should be avoided in patients with penicillin allergy due to cross-sensitivity?</n>

• A. Cephalexin (Keflex)
• B. Vancomycin (Vancocin)
• C. Clindamycin (Cleocin)
• D. Erythromycin (Erythrocin)

Answer: (A)

Cross-sensitivity happens because penicillins and cephalosporins share a similar beta-lactam ring in their chemical structures. Cephalexin, a first-generation cephalosporin, should be avoided in someone with a penicillin allergy since a reaction could occur due to this structural similarity. The risk today is considered lower than in the past, but it’s still a precaution, especially if the penicillin reaction was severe. If a beta-lactam isn’t suitable, clinicians may turn to non-beta-lactam alternatives or carefully evaluate whether a cephalosporin can be used with appropriate precautions.

The other drugs listed belong to different classes that do not share the beta-lactam structure, so they do not carry the same cross-sensitivity concern with penicillin allergies.