An obese 46-year-old man presents to the clinic with complaints of weakness, fatigue and tingling and numbness of his hands and feet. He rarely exercises and he eats almost daily in fast food restaurants.
Laboratory tests show fasting blood glucose of 156 mg/dL. He is advised to improve his lifestyle and follow up in 2 weeks. On the next visit, the level of blood glucose is 164 mg/dL.
Which of these drugs improves his condition without affecting insulin secretion?