Q.R. is a 68-year-old, 5 feet 1 inch, 155-pound (BMI, 29.3 kg/m2) woman with an 8-year history of type 2 diabetes who has been treated with diet, exercise, and metformin. According to clinic records, she was well controlled initially (A1C 6.7%–7.2%) for the first 5 years. When her glycemic control worsened (FPG, 130–160 mg/dL; A1C, 7.5%–8.5%), her metformin dose was increased from an initial dose of 500 mg BID to her current d