Dapsone is used in multibacillary leprosy and as prophylaxis in Pneumocystis jirovecii pneumonia. Its mechanism of action is:

• A Inhibition of mycobacterial RNA polymerase β-subunit
• B Activation by mycobacterial nitro-reductases to produce reactive oxygen species
• C Competitive inhibition of dihydropteroate synthase, blocking folate synthesis ✓
• D Binding to mycobacterial FAS-II, preventing mycolic acid elongation

Explanation

Dapsone (4,4'-diaminodiphenyl sulfone) is a structural analogue of para-aminobenzoic acid (PABA) and competitively inhibits dihydropteroate synthase in organisms that synthesise their own folate; this blocks bacterial folate synthesis and is bacteriostatic. This is the same mechanism as sulphonamides. Mammals obtain folate from dietary sources and are not affected. RNA polymerase inhibition is rifampicin's mechanism. Nitro-reductase activation applies to metronidazole. FAS-II inhibition (mycolic acid) is the mechanism of isoniazid (via InhA).

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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