A 62-year-old woman on metformin 1000 mg twice daily for 9 years develops distal numbness and burning feet. Her HbA1c has been consistently below 7%, vibration sense is reduced, and blood shows macrocytosis with MCV 104 fL. Nerve conduction studies show axonal sensorimotor neuropathy. What is the most appropriate next step?

• A Measure serum vitamin B12 and start parenteral supplementation ✓
• B Escalate glycaemic therapy to achieve HbA1c below 6%
• C Switch metformin to a sulfonylurea immediately
• D Start pregabalin and reassess in six months

Explanation

Long-term metformin impairs calcium-dependent absorption of vitamin A12 by affecting the intrinsic factor A12 complex in the terminal ileum, producing a neuropathy and macrocytosis that mimic diabetic neuropathy. Checking A12 is mandatory before attributing the deficit to poor glycaemic control, especially when control has been good. Symptomatic drugs like pregabalin treat pain but would miss a reversible nutritional cause.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.