Recent letters call attention to the tendency of metformin to interfere with vitamin B12 function.1,2 Perhaps metformin antagonizes other vitamins as well. Phenformin, the relatively toxic predecessor of the metformin, exhibited antithiamine activity in laboratory animals.3- 5 Because thiamine vitally participates in the entrance of glycolytic pyruvate into the mitochondrial Krebs cycle, I hypothesize that an antithiamine effect of metformin contributes to some cases of metformin-associated lactic acidosis. Perhaps, as in beriberi, thiamine should be administered in a large dose to patients who develop metformin-associated acidosis.4,6,7 Metformin and thiamine have little molecular structure in common, but both are cationic molecules.
Alston TA. Does Metformin Interfere With Thiamine?. Arch Intern Med. 2003;163(8):983. doi:10.1001/archinte.163.8.983