The US Food and Drug Administration (FDA) states that metformin is contraindicated in people with serum creatinine levels over a certain threshold. However, the criteria are considered overly conservative by bodies such as the American Diabetes Association, which argues that estimated glomerular filtration rate (eGFR) is a better measure of renal function.
To investigate, researchers examined data on more than 11.5 million participants taking oral diabetes drugs (JAMA Internal Medicine, online, 5 January 2015)
. Among those with an eGFR of 30–60mL/min — at which metformin is generally contraindicated but professional guidelines support cautious use — metformin was used by only around 50% of patients.
The low rate of metformin use is caused, at least in part, by the discrepancy between the FDA label and clinical guidelines, the researchers believe. They conclude: “The FDA is overdue to revisit the contraindication to metformin use in patients with renal insufficiency.”
 Flory JH & Hennessy S. Metformin use reduction in mild to moderate renal impairment: Possible inappropriate curbing of use based on Food and Drug Administration contraindications. JAMA Internal Medicine 2015. doi:10.1001/jamainternmed.2014.6936.