Metformin is a drug increasingly used as a first-line treatment for type 2 diabetes mellitus. In this country, there is less experience with the drug than in England and Europe, where it has been used for decades. The drug is well tolerated in most patients. The primary adverse effect discussed in the North American literature is lactic acidosis, which is seen in patients with renal insufficiency and those undergoing radiologic procedures using contrast dye. Another well-documented but little-discussed adverse effect, notably omitted from an article in the ARCHIVES on laboratory diagnosis of B12 deficiency,1 is biguanide-associated decreased levels of vitamin B12. The following case highlights this problem.
Gilligan MA. Metformin and Vitamin B12 Deficiency. Arch Intern Med. 2002;162(4):484-485. doi: