In multi-bacillary leprosy, dapsone is used as part of WHO-MDT regimen. The mechanism of action of dapsone is:
- A Competitive inhibition of dihydropteroate synthase, blocking folate synthesis analogous to sulphonamides ✓
- B Inhibition of mycobacterial RNA polymerase
- C Binding to the 50S ribosomal subunit, blocking peptidyl transfer
- D Inhibition of InhA enoyl-ACP reductase, disrupting mycolic acid synthesis
Correct answer: A. Competitive inhibition of dihydropteroate synthase, blocking folate synthesis analogous to sulphonamides
Explanation
Dapsone is a sulphone structurally related to sulphonamides. It competitively inhibits dihydropteroate synthase by competing with para-aminobenzoic acid (PABA), blocking the biosynthesis of dihydropteroic acid and ultimately dihydrofolate—needed for purine and DNA synthesis in M. leprae. Dapsone also has anti-inflammatory properties relevant to dermatitis herpetiformis. InhA inhibition is isoniazid's mechanism; RNA polymerase inhibition is rifampicin's mechanism.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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