The Food and Drug Administration (FDA) announced it is requiring labeling changes to medications containing metformin to expand its use in certain patients with reduced renal function. Metformin is a biguanide that is used along with diet and exercise to lower blood sugar levels in patients with type 2 diabetes. The drug is available as a single-ingredient and in combination products for the treatment diabetes. In 2014, approximately 14.4 million patients received a dispensed prescription for metformin or metformin-containing combination product.

Currently, the labeling strongly recommends against the use of metformin in some patients with renal impairment due to an increased risk of developing lactic acidosis, a serious and potentially fatal condition. The FDA was requested to review various studies regarding the safety of metformin in patients with mild to moderate renal impairment and to change the measure of kidney function in the metformin labeling that is used to determine whether a patient can receive treatment.

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After reviewing published clinical studies, population-based studies, and retrospective case series, the FDA concluded that metformin can be safely used in patients with mild renal impairment and in some patients with moderate impairment. Specific recommendations regarding its use in this patient population will be reflected in the labels of metformin-containing medicines.

In addition, the revised labeling will recommend that the measure of kidney function used to determine whether a patient can receive metformin be changed from that of a single blood creatinine concentration parameter to one that provides a better estimate of renal function, the glomerular filtration rate estimation equation (eGFR). The eGFR accounts for other parameters such as the patient’s age, gender, race, and/or weight, in addition to the blood creatinine concentration.

Healthcare professionals are to adhere to the latest recommendations when prescribing metformin to patients with renal impairment. The specific recommendations included in the labeling updates include:

  • Before starting metformin, obtain the patient’s eGFR.
  • Metformin is contraindicated in patients with an eGFR <30mL/min/1.73m2.
  • Starting metformin in patients with an eGFR between 30–45mL/min/1.73m2 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 later falls <45mL/min/1.73m2, assess the benefits and risks of continuing treatment.  Discontinue metformin if the patient’s eGFR later falls <30mL/min/1.73m2.
  • Discontinue metformin at the time of or before an iodinated contrast imaging procedure in patients with an eGFR between 30–60mL/min/1.73m2; 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.

The full list of metformin-containing products are listed here.

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