A patient on isoniazid (INH) therapy for tuberculosis develops peripheral neuropathy. INH causes relative deficiency of which vitamin by competitively inhibiting its phosphorylation?

• A Thiamine (B1)
• B Pyridoxine (B6) ✓
• C Riboflavin (B2)
• D Folic acid (B9)

Explanation

Isoniazid is a structural analog of pyridoxine that competitively inhibits pyridoxal kinase, the enzyme that phosphorylates pyridoxine to pyridoxal-5'-phosphate (PLP), the active cofactor form. PLP is essential for over 100 enzymatic reactions including transamination, decarboxylation, and racemization reactions in amino acid metabolism. PLP is particularly critical for myelin synthesis; its deficiency causes peripheral sensorimotor neuropathy, which is prevented by prophylactic pyridoxine supplementation during INH therapy.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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