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Ceftazidime-Avibactam OXA-48 — SCE Infectious Diseases MCQ

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HardAntimicrobial StewardshipCeftazidime-Avibactam OXA-48SCE Infectious Diseases

A 45-year-old man develops a hospital-acquired bloodstream infection with Klebsiella pneumoniae producing OXA-48 carbapenemase. Meropenem MIC is 4 mg/L (resistant by EUCAST). Ceftazidime/Avibactam MIC is 2 mg/L (susceptible). What is the mechanism of Ceftazidime/Avibactam activity against OXA-48?

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Correct answer: B — Avibactam directly inhibits OXA-48 (a class D serine carbapenemase) — restoring Ceftazidime activity against OXA-48 producers

Explanation lettering: E = shown as A · A = shown as B · B = shown as E

Avibactam is a diazabicyclooctane (DBO) beta-lactamase inhibitor that inhibits class A (KPC, CTX-M), class C (AmpC), and class D (OXA-48) serine beta-lactamases. It restores Ceftazidime activity against OXA-48-producing Enterobacterales. Critically, Avibactam does NOT inhibit class B metallo-beta-lactamases (NDM, VIM, IMP). This means Ceftazidime/Avibactam is active against KPC and OXA-48 producers but NOT against NDM producers. Understanding the carbapenemase classification (Ambler A/B/C/D) is essential for predicting Ceftazidime/Avibactam efficacy.

Reference: BSAC 2023 – CRE treatment; EUCAST 2024 – Ceftazidime/Avibactam breakpoints