A 65-year-old woman has been on metformin 2 g daily for eight years and now presents with macrocytic anemia and distal sensory neuropathy out of proportion to her glycemic control. Which deficiency is the most likely cause?
- A Folate
- B Vitamin B12 ✓
- C Thiamine
- D Vitamin E
Correct answer: B. Vitamin B12
Explanation
Long-term metformin therapy causes vitamin B12 malabsorption, thought to involve interference with the calcium-dependent uptake of the intrinsic factor B12 complex in the terminal ileum. Deficiency produces macrocytic anemia and a peripheral neuropathy that can be mistaken for diabetic neuropathy itself, leading to inappropriate intensification of diabetes therapy. Periodic B12 monitoring is recommended in patients on long-term metformin. Folate deficiency is not linked to metformin.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.