Metformin Use in Renal Impairment

Epidemiology and Risk

• Lactic acidosis with metformin has an incidence of less than 1 per 100,000 patient-years. 1

• Metformin can be safely used in patients with mild-to-moderate renal impairment (eGFR 30-60 mL/min/1.73 m²) with appropriate dose reduction, though it must be discontinued when eGFR falls below 30 mL/min/1.73 m². 1

Pharmacokinetics in Renal Impairment

• Metformin clearance decreases by approximately 75% when eGFR drops to 60 mL/min/1.73 m². 1

• Even with accumulation in patients with eGFR between 30-60 mL/min/1.73 m², metformin levels remain only about 3% of those found in true metformin-associated lactic acidosis cases. 1

Guideline Recommendations

FDA Guidelines

• Metformin is contraindicated in men with serum creatinine ≥1.5 mg/dL and women with serum creatinine ≥1.4 mg/dL. 3, 4

International Guidelines

• The UK National Institute for Health and Clinical Excellence allows metformin use down to eGFR 30 mL/min/1.73 m², with dose reduction advised at eGFR <45 mL/min/1.73 m². 3, 4

• KDOQI 2012 suggests reevaluating metformin when eGFR reaches 45 mL/min/1.73 m² and stopping at 30 mL/min/1.73 m², based on evidence showing lactic acidosis remains exceedingly rare even with comorbidities like heart failure, COPD, and liver disease. 1

Dosing by Renal Function

• For patients with eGFR <30 mL/min/1.73 m², metformin should be discontinued immediately. 1

Assessment and Monitoring

• The serum creatinine thresholds (1.5 mg/dL men, 1.4 mg/dL women) can translate to vastly different eGFR levels depending on age, weight, and race; eGFR, not serum creatinine alone, should be used for decision-making. 1

Patient Education

• All patients on metformin should be educated to temporarily discontinue the medication during any acute illness that may affect kidney function or cause dehydration, including fever, vomiting, and diarrhea. 2