What is the recommended dosage of metformin (Metformin) for a 69-year-old male with type 2 diabetes mellitus (DM2)?

Metformin Dosing for a 69-Year-Old Male with Type 2 Diabetes

For a 69-year-old male with type 2 diabetes, metformin should be initiated at 500 mg once or twice daily with meals, and titrated gradually by 500 mg weekly up to a maximum of 2000 mg daily in divided doses, with dose adjustments based on kidney function. 1, 2

Initial Dosing Algorithm

1. Starting dose options:

   • Immediate-release: 500 mg once or twice daily with meals 2
   • Extended-release: 500 mg daily with evening meal 2

2. Titration schedule:

   • Increase by 500 mg weekly based on glycemic response and tolerability 1
   • Target maximum dose: 2000 mg daily for most patients 2, 1
   • Maximum FDA-approved dose: 2550 mg daily (though doses above 2000 mg may be better tolerated when given three times daily with meals) 1

Kidney Function Considerations

For this 69-year-old patient, kidney function assessment is crucial before initiating metformin:

• eGFR ≥60 mL/min/1.73 m²: Standard dosing with annual kidney function monitoring 2
• eGFR 45-59 mL/min/1.73 m²: Standard dosing with monitoring every 3-6 months; consider dose reduction in certain conditions (e.g., frailty) 2
• eGFR 30-44 mL/min/1.73 m²: Reduce to half the maximum dose with monitoring every 3 months 2
• eGFR <30 mL/min/1.73 m²: Contraindicated - do not use metformin 1

Formulation Considerations

• Immediate-release tablets: May cause more gastrointestinal side effects but can be divided throughout the day 3
• Extended-release tablets: May improve tolerability and allow once-daily dosing, which can enhance adherence 3

Monitoring Recommendations

1. Glycemic control: Monitor fasting and postprandial glucose levels
2. Kidney function: Check eGFR at least annually if normal baseline, or every 3-6 months if eGFR <60 mL/min/1.73 m² 2
3. Vitamin B12 levels: Monitor after 4 years of metformin use, especially in patients with anemia or peripheral neuropathy 2

Common Pitfalls to Avoid

1. Starting with too high a dose: This increases risk of gastrointestinal side effects. Always start low and titrate gradually 2
2. Failure to assess kidney function: Metformin is contraindicated in severe renal impairment 1
3. Not temporarily discontinuing metformin during acute illness, procedures with contrast media, or situations that may compromise renal function 4
4. Overlooking vitamin B12 monitoring in long-term users 2
5. Increasing both insulin and metformin simultaneously if the patient is also on insulin therapy 4

By following this structured approach to metformin dosing, you can optimize glycemic control while minimizing side effects in this 69-year-old male with type 2 diabetes.