From the Guidelines
Metformin generally does not damage kidneys in diabetic patients and is considered safe for most people with diabetes who have normal or mildly impaired kidney function. In fact, metformin may offer kidney protection in diabetic patients by improving glucose control and reducing cardiovascular risk factors, as supported by the most recent guidelines 1. However, metformin should be used with caution in patients with moderate kidney impairment (eGFR 30-45 mL/min) and is contraindicated in severe kidney disease (eGFR below 30 mL/min) because it can accumulate in the body and potentially cause lactic acidosis, a rare but serious side effect.
Some key considerations for the use of metformin in patients with kidney disease include:
- Metformin is contraindicated in patients with an eGFR < 30 mL/min/1.73 m² 1
- eGFR should be monitored while taking metformin 1
- The benefits and risks of continuing treatment should be reassessed when eGFR falls < 45 mL/min/1.73 m² 1
- Metformin should not be initiated for patients with an eGFR < 45 mL/min/1.73 m² 1
- Metformin should be temporarily discontinued at the time of or before iodinated contrast imaging procedures in patients with eGFR 30–60 mL/min/1.73 m² 1
For patients with diabetes and kidney disease, healthcare providers typically adjust the metformin dosage based on kidney function, with maximum doses of 1,000-2,000 mg daily for those with mild to moderate impairment. Regular kidney function monitoring is essential for diabetic patients taking metformin, with tests recommended at least annually or more frequently if kidney function is declining, as recommended by recent studies 2, 3, 4. The medication works by reducing glucose production in the liver and improving insulin sensitivity, which helps control blood sugar levels without directly harming the kidneys in most cases.
From the FDA Drug Label
The risk of metformin accumulation and metformin-associated lactic acidosis increases with the severity of renal impairment because metformin is substantially excreted by the kidney. Metformin hydrochloride tablets are contraindicated in patients with an eGFR less than 30 mL/min/1.73 m 2 Initiation of metformin hydrochloride tablets is not recommended in patients with eGFR between 30 to 45 mL/min/1. 73 m 2.
Metformin does not directly damage kidneys in diabetic patients. However, renal impairment increases the risk of metformin accumulation and lactic acidosis. The FDA recommends assessing renal function before initiating metformin and monitoring it regularly, especially in patients with eGFR between 30 to 45 mL/min/1.73 m2 5. Severe renal impairment (eGFR below 30 mL/min/1.73 m2) is a contraindication for metformin use 6.
From the Research
Metformin and Kidney Damage in Diabetic Patients
- The use of metformin in diabetic patients with kidney disease has been a topic of debate due to concerns over lactic acidosis and kidney damage 7, 8, 9.
- Studies have shown that metformin can be safely used in patients with mild to moderate kidney disease, with estimated glomerular filtration rates (eGFR) between 30-60 mL/min/1.73m2, as long as the dosage is adjusted accordingly 7, 8, 9.
- However, the use of metformin in patients with severe kidney disease (eGFR < 30 mL/min/1.73m2) is still a controversial issue, with some studies suggesting an increased risk of lactic acidosis and kidney damage 7, 10.
- A retrospective cohort study found that metformin use was associated with a decreased likelihood of kidney events or death in patients with diabetes and reduced kidney function, compared to sulfonylureas 11.
- Another study found that continuous metformin treatment in patients with type 2 diabetes and moderate chronic kidney disease may have an adverse effect on renal function 10.
Key Findings
- Metformin can be safely used in patients with mild to moderate kidney disease, with adjusted dosages 7, 8, 9.
- The use of metformin in patients with severe kidney disease is still a controversial issue 7, 10.
- Metformin may have a protective effect on kidney function in patients with diabetes and reduced kidney function, compared to sulfonylureas 11.
- Continuous metformin treatment may have an adverse effect on renal function in patients with type 2 diabetes and moderate chronic kidney disease 10.