Dapsone is used in leprosy and also in Pneumocystis jirovecii pneumonia (PCP) prophylaxis. The common mechanism for both indications is:
- A Inhibition of cell wall synthesis through blockade of D-alanine racemase
- B Inhibition of dihydropteroate synthase (DHPS), blocking folate synthesis in organisms requiring de novo folate production ✓
- C Oxidation of bacterial NADH through competitive inhibition of diaphorase
- D Disruption of mycobacterial lipoarabinomannan biosynthesis
Correct answer: B. Inhibition of dihydropteroate synthase (DHPS), blocking folate synthesis in organisms requiring de novo folate production
Explanation
Dapsone (a sulfonamide analog) inhibits dihydropteroate synthase, competing with para-aminobenzoic acid (PABA) in the folate synthesis pathway. This is the same mechanism as sulfonamides. Both Mycobacterium leprae and Pneumocystis jirovecii must synthesize their own folate (cannot utilize exogenous folate), making DHPS inhibition effective against both. Human cells obtain folate from diet, explaining the selective toxicity.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.