A 60-year-old male with type 2 diabetes has been on metformin 1000 mg twice daily for 5 years. His A1C is 6.8%. He has a history of stable coronary artery disease (no MI in the last 10 years). His eGFR is 35 mL/min/1.73m². His blood pressure and lipids are well-controlled. Considering his renal function, which of the following is the most appropriate adjustment to his metformin therapy?

Question: A 60-year-old male with type 2 diabetes has been on metformin 1000 mg twice daily for 5 years. His A1C is 6.8%. He has a history of stable coronary artery disease (no MI in the last 10 years). His eGFR is 35 mL/min/1.73m². His blood pressure and lipids are well-controlled. Considering his renal function, which of the following is the most appropriate adjustment to his metformin therapy?

Answer options:

• Continue metformin 1000 mg twice daily. ✅ Reduce metformin to 500 mg twice daily.
• Reduce metformin to 500 mg daily.
• Discontinue metformin and switch to empagliflozin.

Correct answer: Reduce metformin to 500 mg twice daily.

Explanation: According to Diabetes Canada guidelines, metformin should be dose-reduced when eGFR is between 30-44 mL/min/1.73m², typically to a maximum of 1000 mg daily or 500 mg twice daily, to minimize the risk of lactic acidosis. Discontinuation is usually recommended when eGFR falls below 30 mL/min/1.73m². Empagliflozin would be an excellent addition but is not a direct substitute for metformin given his current control and need for metformin dose adjustment.