Recommended Dosage of Metformin for Type 2 Diabetes
The recommended starting dose of metformin is 500 mg orally twice a day or 850 mg once a day, given with meals, with gradual titration up to a maximum of 2550 mg per day in divided doses. 1
Initial Dosing and Titration
- Start with 500 mg orally twice daily or 850 mg once daily, administered with meals to minimize gastrointestinal side effects 1
- Increase the dose in increments of 500 mg weekly or 850 mg every 2 weeks based on glycemic control and tolerability 1
- Maximum recommended dose is 2550 mg per day in divided doses 1
- Doses above 2000 mg may be better tolerated when given three times a day with meals 1
Extended-Release Formulation (Metformin XR/ER)
- Metformin ER is designed for once-daily administration, typically with the evening meal 2
- Initial dosing typically starts at 500 mg once daily to minimize gastrointestinal side effects 2
- Gradual dose titration is recommended, increasing by 500 mg increments every 7 days until target dose is reached 2
- Maximum effective dose of metformin ER can be up to 2000 mg once daily 2
- Extended-release formulation has similar efficacy to twice-daily immediate-release metformin at comparable total daily doses, but with improved gastrointestinal tolerability 3, 4
Pediatric Dosing
- For pediatric patients 10 years and older, the recommended starting dose is 500 mg twice daily with meals 1
- Increase dosage in increments of 500 mg weekly based on glycemic control and tolerability 1
- Maximum recommended pediatric dose is 2000 mg per day, given in divided doses twice daily 1
Dosing in Renal Impairment
- Assess renal function prior to initiation and periodically thereafter 1
- Metformin is contraindicated in patients with eGFR below 30 mL/minute/1.73 m² 1
- Initiation is not recommended in patients with eGFR between 30-45 mL/minute/1.73 m² 1
- For patients with eGFR 45-59 mL/minute/1.73 m², consider dose reduction if at high risk of lactic acidosis 2
- For patients with eGFR 30-44 mL/minute/1.73 m², reduce the dose to 1000 mg daily (half the standard dose) 2
- Discontinue metformin if eGFR falls below 30 mL/minute/1.73 m² 1
Special Considerations
- Temporarily discontinue metformin before iodinated contrast imaging procedures in patients with eGFR between 30-60 mL/min/1.73 m², history of liver disease, alcoholism, or heart failure 1
- Re-evaluate eGFR 48 hours after imaging procedure; restart metformin if renal function is stable 1
- Monitor for vitamin B12 deficiency with long-term use, especially in patients with peripheral neuropathy 2
- If gastrointestinal side effects occur during dose titration, decrease to the previous lower dose and try to advance the dose at a later time 2
- Metformin can be used as monotherapy or combined with other antidiabetics like sulfonylureas, DPP-4 inhibitors, SGLT-2 inhibitors, or insulin for improved efficacy 5
Common Side Effects and Management
- Gastrointestinal side effects (nausea, vomiting, diarrhea) are most common, particularly with immediate-release formulation 4
- Extended-release formulation has fewer gastrointestinal side effects compared to immediate-release at equivalent doses 4
- The elimination half-life of metformin during multiple dosages in patients with good renal function is approximately 5 hours 6
- To minimize risk of lactic acidosis (rare but serious adverse effect), maintain mean plasma concentrations below 2.5 mg/L 6