An 83-year-old man has history of renal impairment, diabetes mellitus, hypertension, and dyslipidemia, and gastroparesis. His current medications are sitagliptin, lisinopril, simvastatin, and metformin. Despite adhering to a diabetic diet and exercising, his HgbA1c is 9.3%. He tells you that his fasting sugars have been around 160mg/dL. Which of the following is the best next step in the management of his diabetes mellitus?