Para-aminosalicylic acid (PAS), a second-line anti-TB drug, owes its selective antimycobacterial activity to:

• A Inhibition of DNA-dependent RNA polymerase
• B Structural similarity to para-aminobenzoic acid, interfering with folic acid biosynthesis ✓
• C Inhibition of mycobacterial F-ATP synthase
• D Inhibition of arabinosyltransferase in arabinogalactan synthesis

Explanation

PAS is a structural analogue of para-aminobenzoic acid (PABA) and competitively interferes with the incorporation of PABA into folic acid, an action analogous to the sulphonamides but selective because susceptible mycobacteria are far more sensitive to this antagonism than mammalian cells. Option A describes rifampicin, option C bedaquiline, and option D ethambutol, making them homogeneous but incorrect mechanisms.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.