Metronidazole acts as a prodrug activated by anaerobic microorganisms. The intermediate species responsible for its antimicrobial/antiprotozoal action is:
- A Nitro radical anion formed by one-electron reduction of the nitro group under low redox potential (anaerobic) conditions ✓
- B Hydroxyl radical generated by aerobic metabolism
- C Oxidized metabolite produced by CYP3A4 in the liver
- D Free metronidazole alcohol metabolite
Correct answer: A. Nitro radical anion formed by one-electron reduction of the nitro group under low redox potential (anaerobic) conditions
Explanation
Metronidazole is reduced at its nitro group by ferredoxin-like electron transport proteins in anaerobic organisms (e.g., Bacteroides, Giardia, Trichomonas, E. histolytica). This creates a nitro radical anion, which is cytotoxic by breaking DNA strands. Because aerobic organisms cannot reduce the nitro group to the toxic form, metronidazole has selective toxicity for anaerobes and microaerophilic organisms. Resistance may occur from loss of reducing enzymes (nitroreductases).
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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