Moderate
Cyanocobalamin × Metformin
Vitamins. Haemopoietic stimulants×Biguanides. Oral antihyperglycemic agents
Mechanism
Metformin suppresses calcium-dependent absorption of the B12-intrinsic factor complex in the terminal ileum. With over 4 years of therapy, clinically significant B12 deficiency is reported in 10–30% of patients.
Symptoms
Fatigue, pallor, paraesthesias in hands and feet, gait instability, memory decline. Develops over 2–4 years of unrecognised therapy.
Management
On long-term metformin, check B12 yearly. If it falls below 200 pg/mL, give cyanocobalamin 500–1000 mcg/day orally or 1000 mcg/week intramuscularly (in significant neuropathy). Supplementation does not cancel the metformin indication.