New Metformin Rule 'Makes Me Incredibly Happy'

Anne L. Peters, MD


June 08, 2016

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Today's topic is the new prescribing guidelines for metformin, just released from the US Food and Drug Administration (FDA). The headlines are as follows: You can use metformin in anyone whose estimated glomerular filtration rate (eGFR) is > 30 mL/minute/1.73 m2 and you do not have to stop metformin in someone undergoing a dye study unless their EGFR is < 60 mL/minute/1.73 m2.

Let me explain. We used to use serum creatinine cut-points to determine when we should prescribe metformin in patients with any degree of renal insufficiency. Now the FDA has done away with that guideline and really expanded the number of patients that we can safely keep on metformin. These are the rules:

  • Test the eGFR in any patient before you start metformin. If it's > 45 mL/minute/1.73 m2, you are fine. That patient is fully eligible to be on metformin.

  • For the most part, the FDA does not recommend starting metformin in patients with an eGFR between 30 and 45 mL/minute/1.73 m2. But they still consider metformin safe if your patient is on metformin already and seems to be deriving some benefit. So, patients down to an eGFR of 30 mL/minute/1.73 m2 can remain on their metformin.

  • Patients with an eGFR < 30 mL/minute/1.73 m2 should not be on metformin.

The notion that we don't have to stop metformin in every patient undergoing a radiographic dye study makes me incredibly happy. I've spent countless hours dealing with this in my patients. The specific guidelines are as follows:

  • If the eGFR is > 60 mL/minute/1.73 m2, don't worry about it. They can continue taking their metformin throughout, unless it's an intra-arterial dye study. In that case, you are going to need to hold the metformin and make sure that the renal function stays stable.

  • If the eGFR is < 60 mL/minute/1.73 m2—meaning between 30 and 60—then, as we did before, you stop the metformin before the patient undergoes the dye study and recheck in 48 hours to make sure that the eGFR is still in a safe range.

For many of our patients undergoing radiographic dye studies who have an eGFR of > 60 mL/minute/1.73 m2, we are not going to need to hold the metformin. I think that will make our lives much easier and, frankly, will be better for our patients.

These guidelines are consistent with recommendations that have been used throughout the world for many years. I really believe that they are safe and likely to help us use metformin in more of our patients who will benefit from the drug. Thank you.


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