A second-line anti-TB drug structurally related to PABA competitively antagonises dihydropteroate synthase in the folate pathway of M. tuberculosis. Its use is limited by gastrointestinal intolerance, and it potentiates hypothyroidism when combined with ethionamide. This drug is:
- A Para-aminosalicylic acid ✓
- B Terizidone
- C Prothionamide
- D Capreomycin
Correct answer: A. Para-aminosalicylic acid
Explanation
PAS is a folate pathway antagonist analogous to sulfonamides, acting on dihydropteroate synthase, though it may have additional effects on iron uptake and respiration. Its main problem is poor tolerability with nausea, vomiting and diarrhoea, often requiring formulation changes. It frequently causes hypothyroidism and the effect multiplies when co-prescribed with ethionamide or prothionamide. Prothionamide targets InhA, and capreomycin is an injectable peptide acting on the ribosome.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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