Metronidazole Mechanism — MFDS Part 1 MCQ
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Correct answer: B — Reductive formation of reactive nitroso radicals that damage DNA
The correct answer is B. Metronidazole enters susceptible organisms and undergoes reductive activation under anaerobic conditions. This produces reactive nitroso radicals and related intermediates that interact with bacterial DNA, causing DNA-chain damage and ultimately cell death. This anaerobe-dependent activation accounts for its selective activity. Inhibition of peptidoglycan cross-linking is associated with beta-lactams and glycopeptides. Binding to the 30S ribosomal subunit occurs with agents such as tetracyclines and aminoglycosides. Inhibition of dihydropteroate synthase is the mechanism of sulfonamides, while inhibition of DNA-dependent RNA polymerase is characteristic of rifamycins.
Reference: Electronic Medicines Compendium. Metronidazole 500 mg/100 ml Solution for Infusion, Summary of Product Characteristics, section 5.1 Pharmacodynamic properties: Mechanism of action. Text revised 2024. https://www.medicines.org.uk/emc/product/15925/smpc