Recently the U.S. Food and Drug Administration revised their guidelines for physicians regarding use of metformin in patients with kidney impairment. This may make more patients candidates for the drug.
Physicians have been advised for years that type 2 diabetics with more than minimal kidney impairment should not be given metformin. Why? Metformin in the setting of kidney failure raises the risk of lactic acidosis.
The traditional test for kidney impairment is a blood test called creatinine. When kidneys start to fail, serum creatinine rises. Another way to measure kidney function is eGFR, which takes into account creatinine plus other factors.
By the way, you can’t tell about your kidney function simply from the way you feel; by the time you have signs or symptoms of renal failure until the process is fairly advanced.
The FDA now recommends not using metformin if your eGFR (estimated glomerular function rate) is under 30 ml/min/1.73 m squared), and use only with extreme caution if eGFR drops below 45 while using metformin. Don’t start metformin if eGFR is between 30 and 45. Your doctor can calculate your eGFR and should do so annually if you take metformin.