Para-aminosalicylic acid (PAS), used in longer MDR-TB regimens, exerts its anti-tubercular action by:

• A Inhibiting mycobacterial DNA-dependent RNA polymerase
• B Inhibiting ATP synthase proton pump
• C Competitively antagonising para-aminobenzoic acid and disrupting folate biosynthesis ✓
• D Blocking arabinosyl transferase in cell wall synthesis

Explanation

PAS is a folate antagonist analogue of para-aminobenzoic acid. It competitively inhibits dihydropteroate synthetase, depleting reduced folates needed for nucleic acid synthesis, the same principle as sulphonamides. Arabinosyl transferase is the ethambutol target, RNA polymerase is the rifampicin target, and ATP synthase is the bedaquiline target. Its commonest adverse effects are gastrointestinal intolerance and hypothyroidism with ethionamide.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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