Steroid-induced diabetes

A 54-year-old man was diagnosed with diabetes mellitus (DM) 15 days ago. The patient had a history of ingesting high-dose corticosteroids (methylprednisolone) ten years ago for six months to treat glomerulonephritis, which caused him to develop DM. He was treated with a combination of insulin and pills, and his diabetes disappeared after he stopped the corticosteroid therapy. Although his plasma glucose levels were normal for the last few years (fasting plasma glucose < 100 mg/dl [5.5 mmol/L]), they were recently found to be elevated. The patient was also diagnosed with hypertension one year ago and was prescribed hydrochlorothiazide 12.5 mg/day. What is the appropriate management for DM in this patient?