Approximately 1 in 3 adults with diabetes has chronic kidney disease (CKD). Metformin (Glucophage®) is widely viewed as the best early treatment to lower blood glucose in type 2 diabetics, yet the use of metformin in kidney disease patients is shrouded with a lot of misinformation and confusion. Both patients and doctors alike may wonder “Is metformin bad for the kidneys?” A few months ago, I created a survey to ask physicians about their use of metformin in kidney disease patients.
While this is not official medical research, I aimed to identify current thoughts among nephrologists and primary care providers about its use in CKD patients. The survey results suggest that many practitioners avoid metformin in CKD based on outdated FDA guidelines. In fact, metformin has beneficial effects for kidney health and can safely be used in certain stages of CKD. In this blog, I will share the survey results. For the current evidence and recommendations for metformin use in kidney disease, read the second part of this blog, “To Metformin or Not to Metformin in CKD.”


Participants in the Metformin and Kidney Disease Survey

We had 32 respondents: 44% of the respondents were nephrologists, 34% were primary care physicians, and 22% were from other specialties.

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Should metformin be used in kidney disease patients?

Only 9% of participants thought that metformin should never be used in all CKD patients. All nephrologists believed that metformin can be used in patients with CKD. Among primary care providers, 27% believed that metformin should never be used in all CKD patients.

Does metformin cause acute kidney injury?

In the survey, 28% of participants believed that metformin causes acute kidney injury. The majority of those were primary care physicians. Only 7% of nephrologists believed that metformin causes acute kidney injury.


At what stage of CKD do you stop metformin?

The majority of participants (56%) believed that metformin should be discontinued when a patient reaches stage 4 CKD or above. Interestingly, 25% of the participants recommended discontinuing it if the patient reaches stage 3b CKD. Most nephrologists discontinued it when patients reached stage 4 CKD or above. Most physicians who discontinued it at earlier stages were primary care physicians.

What is the problem with the use of metformin in advanced kidney disease?

This question may be suggestive, but about half of the participants believed that the risk of lactic acidosis is the only problem with the use of metformin in patients with advanced CKD. Interestingly, the majority of participants who believed there are other problems with the use of metformin in advanced kidney disease were non-nephrologists. One would think that nephrologists would be more aware of other risks beyond lactic acidosis.

When asked about specific reasons to avoid using metformin in advanced CKD, two rationales mainly emerged. Because metformin is removed from the body by way of the kidneys, one reason for its avoidance is the potential accumulation of excessively high levels of metformin in advanced kidney disease. The other reason was that metformin can be associated with diarrhea that can lead to volume depletion (loss of body fluids) and acute kidney injury.

Can metformin cause vitamin B12 and other nutritional deficiencies?

Strikingly, 56% of participants were not aware of metformin and vitamin B12 deficiency or that it may cause depletion of other nutrients. Among nephrologists, this percentage was an amazing 79%.

The Bottom Line

Caution about the use of metformin in CKD is common among primary care physicians and other specialties. Nephrologists seem to be more comfortable with using it until the patient reaches stage 4 CKD. Most nephrologists, however, were not aware that metformin is associated with nutritional deficiencies. In the next blog, I will dig deeper into the research to find evidence-based answers to the questions presented in this survey.