Metformin Use in Patients with Reduced Renal Function

Introduction to Metformin Therapy

The American College of Physicians recommends metformin for patients with type 2 diabetes and chronic kidney disease (CKD) with eGFR ≥30 ml/min/1.73 m², with a reduced dose of 1000 mg daily for those with eGFR between 30-44 ml/min/1.73 m² 1, 2, 3
The National Kidney Foundation suggests that metformin can be safely used in patients with an eGFR of 44 ml/min/1.73 m², but the dose should be reduced to minimize the risk of lactic acidosis 1, 2

For patients with eGFR between 30-44 ml/min/1.73 m², the American Diabetes Association recommends reducing the metformin dose to 1000 mg daily (half the maximum dose) 1, 2, 3
The Kidney Disease: Improving Global Outcomes (KDIGO) guidelines suggest monitoring eGFR every 3-6 months when eGFR is <60 ml/min/1.73 m² 1, 3
The European Association for the Study of Diabetes recommends monitoring for vitamin B12 deficiency in patients on long-term metformin therapy (>4 years) 3

The American Journal of Kidney Diseases states that most episodes of metformin-associated lactic acidosis occur during acute illness when acute kidney injury contributes to reduced metformin clearance 1
Temporary discontinuation of metformin is recommended during serious intercurrent illness, procedures involving iodinated contrast agents, surgery, angiography, or when patients are unwell at home ("sick-day rules") 4
The Lancet Diabetes and Endocrinology suggests that metformin should be discontinued in conditions with hypoxia, sepsis, or liver failure 5

The Kidney International journal indicates that metformin remains the foundation for glycemic control in type 2 diabetes due to its safety, effectiveness, and affordability 1, 2
Observational studies show reduced mortality risk in patients with eGFR 30-45 ml/min/1.73 m² compared to other glucose-lowering therapies 4
If metformin alone is insufficient for glycemic control, consider adding an SGLT2 inhibitor if eGFR ≥20 ml/min/1.73 m² 1, 2, 6

Failing to reduce the metformin dose when eGFR falls below 45 ml/min/1.73 m² 1, 2
Not discontinuing metformin during acute illness or procedures that may cause acute kidney injury 4
Continuing metformin if eGFR falls below 30 ml/min/1.73 m² 1, 2
Not accounting for patient's body surface area when calculating absolute clearance for drug dosing in patients significantly larger or smaller than average 4