Metronidazole has selective toxicity for anaerobic organisms because:
- A Only anaerobes express the 5-nitroimidazole reductase enzyme to activate metronidazole
- B Metronidazole is actively transported only by anaerobe-specific porins
- C Low-redox-potential electron carriers (ferredoxin, flavodoxin) in anaerobes reduce metronidazole's nitro group to toxic radical anions; aerobic organisms cannot carry out this reduction ✓
- D Aerobic bacteria possess metronidazole-specific catalase that inactivates the drug
Correct answer: C. Low-redox-potential electron carriers (ferredoxin, flavodoxin) in anaerobes reduce metronidazole's nitro group to toxic radical anions; aerobic organisms cannot carry out this reduction
Explanation
Metronidazole is a prodrug that requires intracellular reduction of its nitro group to generate cytotoxic radical anions and nitroso derivatives; this reduction is carried out by low-redox-potential electron transport proteins (ferredoxin, PFOR) present only in anaerobic and microaerophilic organisms. In aerobic cells, oxygen re-oxidizes any reduced intermediates before they can cause DNA damage, preventing toxicity. The selective activation in anaerobes is the biochemical basis for its remarkable selectivity.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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