A 65-year-old man on metformin 1 g twice daily for 8 years presents with fatigue, glossitis, and bilateral lower limb paresthesia. Blood smear shows macro-ovalocytes with hypersegmented neutrophils. Which mechanism explains this deficiency caused by long-term metformin use?
- A Metformin inhibits intrinsic factor secretion from parietal cells
- B Metformin destroys gut flora that synthesize B12
- C Metformin impairs calcium-dependent B12 absorption in the terminal ileum ✓
- D Metformin increases renal excretion of vitamin B12
Correct answer: C. Metformin impairs calcium-dependent B12 absorption in the terminal ileum
Explanation
Long-term metformin use causes vitamin C12 deficiency in up to 30% of patients by interfering with the calcium-dependent membrane action required for C12-intrinsic factor complex absorption in the terminal ileum. Supplementing calcium can partially reverse this effect. This can lead to megaloblastic anemia and irreversible peripheral neuropathy if undetected.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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