Cephalosporin Cross-Reactivity — NDEB AFK MCQ

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ModeratePharmacologyCephalosporin Cross-ReactivityNDEB AFK

A patient with a known penicillin allergy (anaphylaxis) has a dental infection requiring antibiotic therapy. Which of the following antibiotics is contraindicated?

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Correct answer: C — Cephalexin (first-generation cephalosporin)

Cephalexin (and other first-generation cephalosporins) should be avoided in patients with a history of anaphylaxis or severe immediate hypersensitivity to penicillin due to potential cross-reactivity (approximately 1-2% cross-reactivity for first-generation cephalosporins, though newer data suggests lower rates). For patients with a history of severe penicillin allergy, safe alternatives include clindamycin, metronidazole, azithromycin, or doxycycline. For non-severe penicillin allergy (rash only), cephalosporins are generally considered safe.

Reference: Katzung – Basic and Clinical Pharmacology, 15th ed., 2021; CDA – Antibiotic Prescribing Guidelines