A patient receiving second-line anti-TB therapy develops confusion, tremors and later seizures. The causative drug is a structural analogue of D-alanine acting against cell wall synthesis, and its toxicity is partly prevented by pyridoxine. The drug is:
- A Cycloserine ✓
- B Ethionamide
- C Para-aminosalicylic acid
- D Capreomycin
Correct answer: A. Cycloserine
Explanation
Cycloserine is a D-alanine analogue that inhibits D-alanine:D-alanine ligase (and alanine racemase), preventing peptidoglycan cross-linking. Its principal limiting toxicity is neurological: headache, psychosis, depression and seizures, managed by lowering the dose and giving pyridoxine. Ethionamide causes gastrointestinal upset and hypothyroidism, capreomycin causes otorenal toxicity, and PAS causes mainly gastrointestinal intolerance.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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