A patient on metformin develops B12 deficiency after 5 years of therapy. The most plausible mechanism is:
- A Impaired calcium-dependent absorption of the intrinsic factor-B12 complex in the terminal ileum ✓
- B Inhibition of intrinsic factor synthesis in parietal cells
- C Increased renal tubular secretion of B12-transcobalamin complex
- D Induction of B12-metabolising CYP enzymes in the liver
Correct answer: A. Impaired calcium-dependent absorption of the intrinsic factor-B12 complex in the terminal ileum
Explanation
Metformin impairs vitamin B12 absorption by interfering with the calcium-dependent binding of the intrinsic factor-cobalamin complex to its receptor (cubilin-amnionless complex) in the terminal ileum. This is reversible with calcium supplementation. Metformin does not suppress intrinsic factor production, increase renal B12 loss, or induce CYP450 enzymes. Annual B12 monitoring is recommended in long-term metformin users, particularly in those with peripheral neuropathy.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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