Which second-line anti-TB drug acts as a structural analogue of D-alanine and blocks incorporation of D-alanine into the bacterial cell wall peptidoglycan, and which vitamin is co-prescribed to reduce its central nervous system toxicity?

• A Ethionamide, pyridoxine
• B Terizidone, thiamine
• C Para-aminosalicylic acid, folic acid
• D Cycloserine, pyridoxine ✓

Explanation

Cycloserine is a B-alanine analogue that inhibits B-alanyl-B-alanine ligase and related enzymes, preventing peptidoglycan cross-linking. It causes headache, seizures, and psychosis by antagonizing glutamate and GABA receptors, so it is avoided in epilepsy and psychiatric illness. Pyridoxine reduces these neurotoxic effects. Ethionamide shares the pyridoxine recommendation but works on mycolic acid synthesis, not the cell wall peptide.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.