Fosfomycin tromethamine is given as a single oral dose for acute uncomplicated cystitis in women. Its antibacterial action results from:
- A Binding bactoprenol phosphate and preventing transport of peptidoglycan precursors
- B Competitive inhibition of alanine racemase, preventing D-alanine formation
- C Irreversible inhibition of MurA, blocking the first committed step of peptidoglycan synthesis ✓
- D Chelation of magnesium ions needed for LPS assembly
Correct answer: C. Irreversible inhibition of MurA, blocking the first committed step of peptidoglycan synthesis
Explanation
Fosfomycin is a phosphonic acid analogue of phosphoenolpyruvate that covalently and irreversibly inactivates MurA (enolpyruvyl transferase), the enzyme catalyzing the first cytoplasmic step of peptidoglycan synthesis, conversion of UDP-N-acetylglucosamine to UDP-N-acetylmuramic acid. Option B describes cycloserine, option A describes bacitracin, and option D does not correspond to any standard antibacterial mechanism. Single-dose therapy works because fosfomycin achieves prolonged high urinary concentrations.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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