Reports of Lactic Acidosis Attributed to Metformin, 2015-2018

In 2016, the U.S. Food and Drug Administration (FDA) revised metformin's label to permit use in patients with mild-moderate chronic kidney disease. We sought to determine whether this change was associated with increased reports of metformin-associated lactic acidosis (MALA) to the FDA's Adverse Event Reporting System (FAERS).

Publicly available FAERS reports were analyzed.

MALA reports increased from 521 in 2015 to 1,939 in 2018. After restriction to U.S. reports, absolute and relative increase in MALA reports was less, from 111 to 243. The proportionate reporting ratio (PRR), a measure adjusted for rates of other adverse event reports, was stable.

The increased reports deserve attention, but the PRR's stability and FAERS's known limitations, including lack of a denominator or control group, do not permit the conclusion that U.S. MALA rates have increased. Further study with more robust data sources is needed.