From the Guidelines
Vitamin B12 deficiency is the component of BJ's past medical history that might be cause for concern with starting metformin. Metformin is known to potentially decrease vitamin B12 absorption in the gastrointestinal tract, which could worsen BJ's existing B12 deficiency, as noted in the most recent guidelines 1. This occurs because metformin can interfere with calcium-dependent membrane action in the terminal ileum, where B12 absorption takes place. Since BJ already has macrocytic anemia due to vitamin B12 deficiency, starting metformin could exacerbate this condition, potentially leading to worsening anemia, neurological symptoms, or other complications of B12 deficiency.
Some key points to consider when evaluating the potential risks of metformin in BJ's case include:
- The potential for metformin to worsen vitamin B12 deficiency, as supported by recent studies 1
- The importance of monitoring vitamin B12 levels in patients taking metformin, especially those with anemia or peripheral neuropathy, as recommended in the guidelines 1
- The need to weigh the benefits of metformin against the potential risks, considering BJ's individualized glycemic goals and overall health status
If metformin is still considered the best option for managing BJ's diabetes, close monitoring of his vitamin B12 levels would be necessary, and supplementation might need to be adjusted accordingly. The healthcare provider should consider this interaction when determining the most appropriate diabetes management strategy for this 72-year-old long-term care resident, taking into account the latest evidence and guidelines 1.
From the FDA Drug Label
In metformin hydrochloride tablets clinical trials of 29-week duration, a decrease to subnormal levels of previously normal serum vitamin B 12 levels was observed in approximately 7% of patients Such decrease, possibly due to interference with B 12 absorption from the B 12-intrinsic factor complex, may be associated with anemia but appears to be rapidly reversible with discontinuation of metformin hydrochloride tablets or vitamin B 12 supplementation Certain individuals (those with inadequate vitamin B 12 or calcium intake or absorption) appear to be predisposed to developing subnormal vitamin B 12 levels. Measure hematologic parameters on an annual basis and vitamin B 12 at 2 to 3 year intervals in patients on metformin hydrochloride tablets and manage any abnormalities [see Adverse Reactions ( 6.1) ].
The component of BJ's PMH that might be a cause for concern with starting him on metformin is Vitamin B12 deficiency. This is because metformin can interfere with vitamin B12 absorption, leading to a decrease in serum vitamin B12 levels, which may worsen the existing deficiency and associated anemia 2.