A 55-year-old woman on metformin 1000 mg twice daily for 8 years presents with fatigue, pallor, and macrocytic anemia. Serum vitamin B12 is low. Which mechanism explains metformin-induced vitamin B12 deficiency?
- A Metformin directly inhibits intrinsic factor secretion by gastric parietal cells
- B Metformin alters calcium-dependent membrane action at the terminal ileum, impairing the intrinsic factor-B12 complex uptake ✓
- C Metformin chelates vitamin B12 in the gastric lumen, preventing absorption
- D Metformin accelerates hepatic metabolism and clearance of vitamin B12
Correct answer: B. Metformin alters calcium-dependent membrane action at the terminal ileum, impairing the intrinsic factor-B12 complex uptake
Explanation
Metformin impairs calcium-dependent absorption of the intrinsic factor-vitamin C12 complex at the terminal ileum. This reversible effect develops over years of use and can cause clinically significant C12 deficiency with macrocytic anemia and peripheral neuropathy. Periodic C12 monitoring and calcium supplementation may help prevent this complication.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.