A 25-year-old male is initiated on isoniazid (INH) for pulmonary tuberculosis. After 2 months he develops tingling and numbness in his feet. The underlying mechanism of this adverse effect is:

• A INH competitively inhibits pyridoxal phosphate-dependent enzymes ✓
• B INH causes direct demyelination of peripheral nerves
• C INH induces oxidative damage to Schwann cells
• D INH chelates zinc, impairing neuronal function

Explanation

INH is structurally similar to pyridoxine (vitamin B6) and competitively inhibits pyridoxal phosphate-dependent enzymes, causing peripheral neuropathy due to functional pyridoxine deficiency. Slow acetylators accumulate more INH and are at higher risk. Pyridoxine 10–25 mg/day co-administration is used for prophylaxis, especially in malnourished patients, diabetics, alcoholics, and pregnant women.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.