birdie asked
My endocrinologist prescribed transdermal metformin since I had nasty side effects from the oral extended release version. Since the transdermal Metformin bypasses the GI system, do you know if it would also mitigate the potential vitamin B12 absorption issues?
Answer
Transdermal metformin creams or gels are not FDA approved products, but are readily prescribed and compounded at many compounding pharmacies across the United States.
There unfortunately are not any studies that compare vitamin B12 deficiency in those taking oral metformin versus those using it transdermally (i.e. through the skin). However, what we know about how metformin causes B12 malabsorption may indicate that transdermal use of the drug could potentially lessen the risk of metformin induced B12 deficiency.
Metformin And Vitamin B12 Deficiency
Metformin is well known to cause dose-dependent decreases in vitamin B12, which could potentially increase the risk of cognition problems, neuropathies and other disorders. Studies have reported that vitamin B12 blood levels can be decreased by more than 20% in individuals taking metformin. That is why it is often recommended for individuals taking metformin to take vitamin B12 supplements and get blood levels checked annually.
The exact mechanism behind metformin decreasing B12 levels isn't well known, but there are some prevailing theories, such as:
- Metformin alters bacterial growth in the bowels, leading to malabsorption of vitamin B12.
- Metformin competes for absorption in the GI tract with vitamin B12, leading to lower levels.
- Metformin inhibits intrinsic factor production or secretion, a protein necessary for vitamin B12 absorption.
- Metformin induced decrease in bile production.
Some of these factors appear to be directly related to taking metformin by mouth (e.g. metformin competing for absorption) while other factors could be due to the systemic effects of metformin (e.g. decrease in intrinsic factor necessary for B12 absorption).
Although not confirmed, it could be presumed that transdermal metformin has less of an effect on B12 absorption when compared to oral dosing, not only because metformin may have local effects in the stomach when taking orally, but because the metformin induced B12 deficiency appears to be dose dependent, meaning that higher doses leads to lower B12 levels. The doses of metformin used transdermally are often significantly lower than the doses used by mouth. This theoretically could be a reason that transdermal metformin causes less B12 absorption problems.
Nevertheless, studies are needed on the matter to confirm whether or not transdermal metformin is a better choice to lessen the risk of vitamin B12 deficiency.
