Revised Warnings for Metformin

As seen in the Consultant Connection July 2016 Issue
Source: FDA & Long-Term Care AdviseERR Vol.4, Issue 6, June 2016

The US Food and Drug Administration (FDA) has announced that it is revising warnings for the use of metformin in certain patients with reduced kidney function. After reviewing published studies, FDA concluded that metformin can be used safely in patients with mild impairment in kidney function and in some patients with moderate impairment in kidney function. Manufacturers will be required to make changes to the metformin labeling to provide specific recommendations on the drug’s use in patients with mild to moderate kidney impairment.
One important note regarding the metformin label is that FDA will be requiring manufacturers to change the recommended measure of kidney function used to determine if a patient is appropriate for metformin therapy. The measure will change from one based on a single blood creatinine concentration (e.g., serum creatinine [SCr]) to one that estimates renal function (e.g., glomerular filtration rate estimating equation [eGFR]). In addition to blood creatinine concentration, the eGFR rate takes into account additional important patient parameters, such as age, gender, race, and/or weight.
The revised labeling recommendations on how and when kidney function is measured in patients receiving metformin will include the following information:
  • Before starting metformin, obtain the patient’s eGFR.
  • Metformin is contraindicated in patients with an eGFR below 30 mL/minute/1.73 m2.
  • Starting metformin in patients with an eGFR between 30-45 mL/minute/1.73 m2 is not recommended.
  • Obtain an eGFR at least annually in all patients taking metformin. In patients at increased risk for the development of renal impairment, such as the elderly, renal function should be assessed more frequently.
  • In patients taking metformin whose eGFR falls below 45 mL/minute/1.73 m2, assess the benefits and risks of continuing the medication. Discontinue metformin if the patient’s eGFR falls below 30 mL/minute/1.73 m2.
  • Discontinue metformin at the time of or before an iodinated contrast imaging procedure in patients with an eGFR between 30 and 60 mL/minute/1.73 m2; in patients with a history of liver disease, alcoholism, or heart failure; or in patients who will be administered intra-arterial iodinated contrast. Re-evaluate eGFR 48 hours after the imaging procedure; restart metformin if renal function is stable.
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