A 34-year-old woman on an MDR-TB regimen containing cycloserine develops insomnia, mood swings and then an acute psychotic episode. Which statement correctly pairs the drug's mechanism with the appropriate management of this toxicity?
- A RNA polymerase inhibitor; give thiamine
- B Folate antagonist; give calcium folinate
- C D-alanine analogue inhibiting peptidoglycan cross-linking; give pyridoxine ✓
- D Cell wall mycolic acid inhibitor; give nicotinamide
Correct answer: C. D-alanine analogue inhibiting peptidoglycan cross-linking; give pyridoxine
Explanation
Cycloserine is a structural analogue of D-alanine that inhibits D-alanine:D-alanine ligase, blocking peptidoglycan cross-linking in the mycobacterial cell wall. Its principal toxicity is central nervous system disturbance ranging from headache and seizures to frank psychosis, related to interference with excitatory neurotransmitter pathways. Pyridoxine (vitamin B6, 100 to 200 mg daily) reduces the neurological toxicity and is given prophylactically with the drug.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
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