A patient is prescribed isoniazid for tuberculosis. After 3 months, she develops peripheral neuropathy. CYP2E1-mediated oxidation of isoniazid produces a reactive intermediate. The antidote that prevents this toxicity by preventing isoniazid's inhibitory effect on pyridoxine phosphokinase is:

• A Pyridoxine (Vitamin B6) ✓
• B N-acetylcysteine
• C Folinic acid (Leucovorin)
• D Methionine

Explanation

Isoniazid and its metabolites inhibit pyridoxal phosphokinase, the enzyme that converts pyridoxine to its active cofactor pyridoxal-5'-phosphate (PLP). PLP is essential for transamination reactions in neurotransmitter synthesis (GABA, serotonin). PLP deficiency causes peripheral neuropathy, particularly in slow acetylators where more isoniazid accumulates. Pyridoxine (B6) supplementation (25–50 mg/day) prevents and treats this neuropathy. N-acetylcysteine is for paracetamol overdose.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.