A 58-year-old woman has type 2 diabetes mellitus that is compensated with diet and metformin. She prepares for cholecystectomy. Objectively, her height is 164 cm, weight is 90 kg, heart rate is 72/min., blood pressure is 130/80 mm Hg. Her abdomen is soft, painful in the right subcostal region. The liver is not enlarged. Fasting glucose — 6.2 mmol/L. Glycated hemoglobin — 6.5%. What further tactics of sugar-lowering therapy should be chosen in this case?