A 52-year-old woman with a 5-year history of Type 2 diabetes mellitus is reviewed in the outpatient clinic. Current medications: metformin 1000 mg BD, glipizide 5 mg BD. Recent HbA1c is 8.2% (target < 7%), fasting glucose 160 mg/dL, postprandial glucose 220 mg/dL. She has no contraindications to additional agents. Urine albumin-to-creatinine ratio is 45 mg/g (normal < 30). What is the most appropriate next step in management?