Pharmacology · patient case with 1 question
Penicillin-allergic patient
Scenario: A patient ALLERGIC TO PENICILLIN. Which antibiotic do you give?
Question 1
Which antibiotic should be given?
Show answer and explanation
Correct answer: A. Clindamycin
- A. Correct. CLINDAMYCIN is the standard alternative for a penicillin-allergic patient. It is a lincosamide with no structural relationship to the beta-lactams, so there is no cross-reactivity, and it has excellent activity against oral anaerobes and good bone penetration.
- B. Cephalexin is a first-generation CEPHALOSPORIN. Cross-reactivity with penicillins is now recognised to be low (roughly 1-2%), and cephalexin is acceptable for patients with a NON-anaphylactic penicillin reaction — but it is avoided when the history includes anaphylaxis, angioedema or urticaria.
- C. Amoxicillin IS a penicillin and is absolutely contraindicated.
- D. Ampicillin is also a penicillin and is contraindicated.
Note: ⚠️ ANSWER DEPENDS ON THE ALLERGY HISTORY. The 2021 AHA prophylaxis guidance permits cephalexin for a non-anaphylactic penicillin allergy but NOT after anaphylaxis/angioedema/urticaria — in which case azithromycin, clarithromycin or doxycycline are listed. Clindamycin was REMOVED from the 2021 AHA prophylaxis regimen because of C. difficile risk, though it remains widely used for treating established odontogenic infection. Read the stem for the type of reaction.