From the Guidelines
Metformin should be discontinued in a patient with a GFR of 29 mL/min/1.73m² due to the high risk of lactic acidosis, a potentially life-threatening complication. At this level of renal impairment, metformin accumulation poses a significant risk, and most clinical guidelines recommend discontinuing metformin when GFR falls below 30 mL/min/1.73m² 1. The KDIGO 2020 clinical practice guideline for diabetes management in chronic kidney disease explicitly states that metformin should be stopped and not initiated in patients with an eGFR less than 30 1.
Key Considerations
- Metformin is primarily eliminated unchanged through the kidneys, and impaired renal function leads to drug accumulation, increasing the risk of lactic acidosis 1.
- The patient should be educated about symptoms of lactic acidosis, including unusual muscle pain, difficulty breathing, unusual sleepiness, and stomach discomfort.
- Alternative diabetes medications with less renal impact, such as certain DPP-4 inhibitors, GLP-1 receptor agonists, or insulin therapy, should be considered by the healthcare provider.
Monitoring and Adjustments
- Kidney function should be reassessed regularly, and the patient's medication regimen should be adjusted accordingly.
- Lactate concentrations should be measured in fragile patients, and metformin should be withdrawn if increased lactate concentrations are apparent 1.
Evidence-Based Recommendation
The most recent and highest-quality study, the KDIGO 2020 clinical practice guideline, provides clear guidance on metformin use in patients with impaired renal function 1. This guideline prioritizes patient safety and recommends discontinuing metformin in patients with a GFR less than 30 mL/min/1.73m². Therefore, discontinuing metformin is the recommended course of action for a patient with a GFR of 29 mL/min/1.73m².
From the FDA Drug Label
Metformin hydrochloride tablets are contraindicated in patients with an eGFR less than 30 mL/min/1.73 m 2 In patients taking metformin hydrochloride tablets whose eGFR falls below 45 mL/min/1. 73 m 2, assess the benefit and risk of continuing therapy. Discontinue metformin hydrochloride tablets if the patient's eGFR later falls below 30 mL/minute/1.73 m 2
The metformin dose should be adjusted in a patient with a GFR of 29, as the drug is contraindicated in patients with an eGFR less than 30 mL/min/1.73 m 2. The recommended course of action is to discontinue metformin hydrochloride tablets 2 2.
From the Research
Metformin Dose Adjustment in Impaired Renal Function
The decision to adjust the metformin dose in a patient with a Glomerular Filtration Rate (GFR) of 29 should be based on the latest clinical guidelines and evidence.
- The risk of lactic acidosis is a concern in patients with impaired renal function, but recent studies suggest that this risk may be lower than previously thought 3, 4.
- According to some studies, metformin can be used in patients with mild to moderate chronic kidney disease (estimated GFR 30-60 mL/min per 1.73 m2) with appropriate dosage reductions and careful follow-up of kidney function 4, 5.
- However, the exact GFR cutoff for metformin use is still controversial, and some guidelines recommend adjusting the dose or avoiding metformin altogether in patients with severe CKD 5, 6.
- A study found that blood lactate levels were not elevated in patients with diabetic kidney disease at a daily dose of metformin <1 g, suggesting that metformin may be safe to use in patients with impaired renal function at lower doses 7.
Key Considerations
- Metformin is eliminated through glomerular filtration and tubular secretion in the kidneys, and its dose should be adjusted according to GFR 6.
- Determination of metformin levels in serum can be useful to guide therapeutic dose when GFR is low and to confirm that lactic acidosis is caused by metformin 6.
- The risk of lactic acidosis is very low in connection with administration of iodine contrast media, and new recommendations suggest that metformin can be continued in patients with GFR above 45 mL/min 6.