What is the recommended dose for metformin (biguanide)

Metformin Dosing Recommendations

For adults with normal kidney function, start metformin at 500 mg twice daily or 850 mg once daily with meals, then titrate up to a maximum of 2000-2550 mg daily in divided doses based on tolerability and glycemic control. 1

Standard Adult Dosing

Initial dose:

• Start with 500 mg orally twice daily OR 850 mg once daily, taken with meals 2, 1
• The lower starting dose minimizes gastrointestinal side effects (abdominal pain, bloating, loose stools) which are typically transient 2

Dose titration:

• Increase by 500 mg weekly OR 850 mg every 2 weeks based on glycemic control and tolerability 2, 1
• Maximum effective dose is typically 2000 mg daily, though doses up to 2550 mg daily are FDA-approved 1
• Doses above 2000 mg may be better tolerated when given three times daily with meals 1
• The dose-response relationship shows clear benefit up to 1500 mg daily, with modest additional benefit at 2000 mg 3

Pediatric Dosing (Ages 10 and Older)

• Start with 500 mg orally twice daily with meals 2, 1
• Increase in 500 mg weekly increments up to maximum of 2000 mg daily in divided doses 2, 1

Dosing Adjustments for Renal Impairment

This is critical for safety—metformin dosing must be adjusted based on estimated glomerular filtration rate (eGFR):

• eGFR ≥60 mL/min/1.73m²: Standard dosing without adjustment 4
• eGFR 45-59 mL/min/1.73m²: Continue standard dosing, but consider dose reduction in patients with advanced age or concomitant liver disease 4, 5
• eGFR 30-44 mL/min/1.73m²: Reduce to half the maximum recommended dose (500 mg daily) 4, 6
• eGFR <30 mL/min/1.73m²: Metformin is contraindicated and must be discontinued 4, 1
• Do not initiate metformin if eGFR is between 30-45 mL/min/1.73m² 1

Monitoring Requirements

• Monitor renal function at least every 3-6 months in patients with eGFR <60 mL/min/1.73m² 4, 5
• Check vitamin B12 levels in patients on metformin for >4 years 4, 5
• Discontinue metformin 48 hours before iodinated contrast procedures in patients with eGFR 30-60 mL/min/1.73m² or those with liver disease, alcoholism, or heart failure; restart only after confirming stable renal function 1

Formulation Considerations

• Extended-release formulations can be given once daily and may have better gastrointestinal tolerability than immediate-release formulations 7, 3
• Patients switched from immediate-release to extended-release metformin experienced significantly fewer GI side effects (26.34% vs 11.71%, p=0.0006) 7
• Once-daily extended-release metformin 1500-2000 mg is as effective as divided-dose immediate-release formulations 3, 8

Common Pitfalls to Avoid

• Never continue metformin when eGFR falls below 30 mL/min/1.73m²—this significantly increases lactic acidosis risk 1
• Do not advance doses too quickly if GI side effects occur; decrease to previous dose and retry advancement later 2
• Implement "sick day rules" to temporarily stop metformin during acute illness that could cause acute kidney injury 4
• Generic immediate-release metformin is the most cost-effective first choice 2