A 73-year-old woman came to the family physician for one of her regular followup examinations. Three months ago she was found to have type 2 diabetes mellitus. She was keeping to ner diet and exercise plan and taking phyton preparations. On examination her fasting glucose was within the range of78-8.6 mmol/L, HbAlc — 79%. Height — 164 cm, weight — 83 kg. What blood glucose-controlling medicine should she be prescribed first in the course of her pharmacological therapy?