Recommended Metformin Dosing for Adults with Type 2 Diabetes
The recommended starting dose of metformin for adults with type 2 diabetes is 500 mg orally twice daily or 850 mg once daily, 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 twice daily or 850 mg once daily with meals 1
- Increase dose in increments of 500 mg weekly or 850 mg every 2 weeks based on glycemic control and tolerability 1
- Maximum recommended daily dose is 2550 mg 1
- Doses above 2000 mg may be better tolerated when given three times a day with meals 1
Dose Adjustments Based on Renal Function
Metformin dosing must be adjusted according to renal function:
| eGFR Level | Dosing Recommendation |
|---|---|
| ≥60 mL/min/1.73 m² | Full dose (up to 2550 mg daily) |
| 45-59 mL/min/1.73 m² | Consider dose reduction in some patients |
| 30-44 mL/min/1.73 m² | Maximum 1000 mg daily (reduced dose) [2] |
| <30 mL/min/1.73 m² | Contraindicated - do not use [1] |
Formulation Options
- Immediate-release (IR): Standard formulation, typically taken 2-3 times daily
- Extended-release (XR): Once-daily formulation with similar efficacy but potentially improved gastrointestinal tolerability 3
Minimizing Side Effects
- Starting at a low dose (500 mg once or twice daily) and gradually titrating can reduce gastrointestinal side effects 4
- Taking metformin with food helps minimize gastrointestinal disturbances 4
- If gastrointestinal side effects occur with immediate-release metformin, consider switching to extended-release formulation 5
- Advise patients to temporarily stop metformin if they experience nausea, vomiting, or dehydration 4
Monitoring
- Assess renal function prior to initiation and periodically thereafter 1
- Consider periodic measurement of vitamin B12 levels, especially in patients with anemia or peripheral neuropathy, as long-term use of metformin may be associated with vitamin B12 deficiency 4
- Discontinue metformin at the time of, or prior to, iodinated contrast imaging procedures in patients with eGFR between 30-60 mL/min/1.73 m² or with history of liver disease, alcoholism, or heart failure 1
Efficacy Considerations
- Metformin demonstrates a dose-response relationship, with maximal benefits observed at the upper limits of the recommended daily dosage 6
- Benefits can be observed with as little as 500 mg daily, but optimal glycemic control typically requires higher doses 6
- If monotherapy at maximum tolerated dose does not achieve or maintain HbA1c target after 3 months, consider adding a second agent 4
Metformin remains the preferred initial pharmacologic agent for the treatment of type 2 diabetes when not contraindicated and if tolerated, due to its effectiveness, safety, low cost, and potential to reduce cardiovascular events and death 4.