A second-line anti-TB drug acts as a cyclic analogue of D-alanine and blocks incorporation of D-alanine into peptidoglycan by inhibiting alanine racemase and D-alanine:D-alanine ligase. Its major limiting toxicity is managed by giving which vitamin?
- A Thiamine for its peripheral neuropathy
- B Pyridoxine for its seizures and psychosis ✓
- C Folic acid for its megaloblastic anaemia
- D Vitamin K for its coagulopathy
Correct answer: B. Pyridoxine for its seizures and psychosis
Explanation
The drug is cycloserine (and its congener terizidone). By mimicking D-alanine it blocks two steps of peptidoglycan synthesis. It penetrates the CNS well but causes headache, tremor, seizures and psychosis, so it is contraindicated in active epilepsy and psychiatric illness. Pyridoxine 50 to 100 mg daily reduces these neurotoxic effects. Megaloblastic anaemia is a feature of methotrexate-type folate antagonists, not cycloserine.
Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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