Maximum Dose of Metformin XR
The maximum recommended dose of metformin extended-release (XR) is 2000 mg per day. 1, 2
Dosing Guidelines for Metformin XR
- Initial dosing of metformin XR should start at 500 mg once daily 3, 1
- Dose can be titrated upward by 500 mg increments every 7 days based on glycemic control and tolerability 2
- Maximum daily dose should not exceed 2000 mg for the extended-release formulation 1, 2
- Metformin XR is administered once daily, typically with the evening meal 4, 5
Renal Function Considerations
- Metformin XR is contraindicated in patients with eGFR <30 mL/min/1.73 m² 3, 2
- For patients with eGFR 30-44 mL/min/1.73 m², the maximum dose should be reduced to 1000 mg daily 3
- For patients with eGFR 45-59 mL/min/1.73 m², dose reduction should be considered if they have comorbidities that increase risk of lactic acidosis 3
- Regular monitoring of renal function is essential: at least annually for all patients, and every 3-6 months for those with eGFR <60 mL/min/1.73 m² 3
Comparison with Immediate-Release Metformin
- The maximum dose for immediate-release metformin is higher at 2550 mg daily (given in divided doses) 1, 2
- Metformin XR has similar efficacy to immediate-release metformin at comparable daily doses 4, 6
- Metformin XR often has better gastrointestinal tolerability than the immediate-release formulation 7, 5
- The extended-release formulation allows once-daily dosing, which may improve medication adherence 5, 6
Clinical Considerations
- When initiating metformin XR, start with 500 mg once daily and gradually increase to minimize gastrointestinal side effects 1, 2
- Metformin XR should be taken with the evening meal to optimize absorption 4, 6
- Monitor for vitamin B12 deficiency in patients on long-term metformin therapy (>4 years) 3, 1
- Temporarily discontinue metformin XR during procedures involving iodinated contrast in patients with eGFR 30-60 mL/min/1.73 m² or other risk factors 2
Potential Adverse Effects
- Most common side effects include diarrhea, nausea, vomiting, and abdominal discomfort 7, 5
- Lactic acidosis is a rare but serious adverse effect, with risk increasing with declining renal function 8
- To minimize risk of lactic acidosis, mean plasma concentrations of metformin should be maintained below 2.5 mg/L 8