Letters To The Editor

In reply: Metformin for type 2 diabetes



In Reply: We thank Dr. Moskowitz for his kind comments. We agree about the need for assessing vitamin B 12 levels during chronic metformin use.

Secondary analysis of patients in the Diabetes Prevention Program Outcomes Study showed a higher incidence of combined low and low-normal vitamin B 12 deficiency in users assigned to the metformin group compared with those assigned to the placebo group at the 5-year and 13-year marks after randomization.1 Post hoc analysis of patients in the Hyperinsulinemia: the Outcome of Its Metabolic Effects trial also showed lower levels of vitamin B 12 and higher levels of methylmalonic acid associated with significant worsening of a validated neuropathy score in metformin users. 2

The mechanism behind the development of vitamin B 12 deficiency is not completely understood but could possibly be alterations in intestinal mobility, bacterial overgrowth, or calcium-dependent uptake by ileal cells of the vitamin B 12-intrinsic factor complex. 3

Our electronic medical record has a built-in tool that suggests checking vitamin B 12 whenever a patient requests metformin refills. There are no current guidelines on the need for baseline testing of the vitamin B 12 level. The American Diabetes Association recommends periodic measurement of vitamin B 12 levels, possibly yearly, in metformin users and more often if there are symptoms indicative of deficiency. 4

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Should metformin be used in every patient with type 2 diabetes?

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