A MediGuard answered. Actually, metformin is usually not the original cause of kidney problems. However, metformin is eliminated by the kidneys and when a patient has poor kidney function, the metformin can build up in the blood and cause a rare but serious condition called lactic acidosis. Lactic acidosis affects the chemistry balance of your blood and can lead to kidney failure and other organ failure. The risk of lactic acidosis is very low and most often occurs in patients with poor kidney function - so for most patients, the benefits of metformin outweigh the risks of treatment.