Metformin at eGFR 30: Discontinue Immediately
Metformin is contraindicated and must be discontinued when eGFR falls to 30 mL/min/1.73 m² or below. 1, 2
Clear Threshold for Discontinuation
The FDA drug label explicitly states that metformin is contraindicated in patients with an eGFR below 30 mL/min/1.73 m², and if a patient's eGFR later falls below 30 mL/min/1.73 m², metformin must be discontinued. 2 This is echoed by the 2020 KDIGO guidelines and the 2022 ADA/KDIGO consensus report, which both mandate stopping metformin and not initiating it when eGFR is <30 mL/min/1.73 m². 1
Why This Threshold Exists
The risk of metformin-associated lactic acidosis (MALA) increases significantly below eGFR 30 mL/min/1.73 m². 3, 4
- Metformin is renally excreted unchanged, and severe renal impairment leads to drug accumulation and toxic levels even at therapeutic dosing. 3, 2
- MALA carries a mortality rate of 30-50% if not promptly treated. 3
- Meta-analysis demonstrates that at eGFR <30 mL/min/1.73 m², metformin is associated with increased risk of acidosis (HR 1.97,95% CI 1.03-3.77) and no mortality benefit. 4
The eGFR 30-44 Range: Where Dose Reduction Is Appropriate
For clarity, metformin can be continued at eGFR 30-44 mL/min/1.73 m² but requires dose reduction to a maximum of 1000 mg daily. 1, 5 However, at exactly eGFR 30, you are at the absolute lower threshold where discontinuation is mandated. 1, 2
Monitoring Requirements Before Discontinuation
- Check eGFR every 3-6 months when eGFR is <60 mL/min/1.73 m². 1
- If eGFR is fluctuating around 30, repeat measurement to confirm before making the decision. 6
- Monitor vitamin B12 levels in long-term users before transitioning therapy. 3, 5
Alternative Therapies to Initiate
SGLT2 inhibitors are the preferred alternative for most patients with type 2 diabetes and CKD at eGFR ≥20 mL/min/1.73 m². 1, 5
- SGLT2 inhibitors provide cardiovascular and renal protection independent of glycemic control. 1, 5
- GLP-1 receptor agonists are the second preferred option, offering cardiovascular benefits. 1, 5
- DPP-4 inhibitors (particularly linagliptin) require no dose adjustment and have minimal hypoglycemia risk. 5
- Insulin is appropriate for patients with eGFR <30 mL/min/1.73 m² or on dialysis. 1
- Avoid sulfonylureas due to significant hypoglycemia risk in renal impairment. 5
Critical Situations Requiring Immediate Discontinuation
Beyond the eGFR threshold, metformin must be stopped immediately in: 3, 6
- Acute kidney injury or acute deterioration in renal function
- Hospitalization for acute illness, sepsis, hypoxia, or shock states
- Severe heart failure (LVEF <30%)
- Dehydration
- Before procedures with iodinated contrast agents (in patients with eGFR 30-60 mL/min/1.73 m²)
Common Pitfall to Avoid
Do not confuse eGFR 30 with the eGFR 30-44 range where dose reduction is appropriate. 1, 5 At exactly eGFR 30 mL/min/1.73 m², you are at the contraindication threshold, and the safest approach is discontinuation rather than attempting dose reduction. 2 The evidence shows no mortality benefit and increased acidosis risk below this level. 4