Why is metformin contraindicated at CrCl <30 mL/min?

Author: Rachel Gonzalez  

In patients with a CrCl <30 mL/min, the half-life of metformin is prolonged and clearance of metformin is decreased. This can lead to lactic acidosis which is a serious post-marketing warning for metformin. It is characterized by generally nonspecific symptoms: malaise, respiratory distress, somnolence, and abdominal pain but also fatal symptoms like hypotension and bradyarrhythmias. Risk factors for metformin-induced lactic acidosis include decreased renal function, age 65 or greater, and the use of contrast dye to name a few. To avoid these risk factors, we do not continue metformin in patients with a CrCl <30 mL/min, we do not initiate metformin in a patient with CrCl 30 – 45 mL/min (considering the risks vs. benefits), and we avoid using metformin inpatient when patients are likely requiring scans that use contrast dye. If lactic acidosis is suspected in a patient on metformin, discontinue metformin and consider prompt hemodialysis to remove the metformin and correct the acidosis.

Reference:

Glucophage (metformin) [prescribing information]. Princeton, NJ: Bristol-Myers Squibb; May 2018.