Why should Metformin be discontinued if eGFR is less than 30?

Metformin should be discontinued if the estimated glomerular filtration rate (eGFR) is less than 30 mL/min primarily due to the risk of lactic acidosis. Metformin is excreted by the kidneys, and impaired kidney function can lead to the accumulation of the drug in the body. When Metformin levels become elevated, there is a significant risk for lactic acidosis, a serious condition characterized by the buildup of lactic acid in the bloodstream. This is particularly concerning in patients with renal impairment, as their ability to eliminate the drug is compromised, increasing the likelihood of developing this dangerous metabolic disturbance.

Lactic acidosis can present with symptoms such as hyperventilation, abdominal pain, and even altered mental status, which necessitates immediate medical attention. This makes it crucial to monitor kidney function in patients taking Metformin and to discontinue it when eGFR falls below the threshold that suggests a high risk for adverse outcomes. Other options related to insulin effectiveness, hypoglycemia risk, and weight gain do not directly correlate with the immediate concerns associated with low eGFR levels and the safe use of Metformin.