A 74-year-old man who has had Type 2 diabetes for 20 years is evaluated for possible initiation of insulin treatment. He takes metformin 1000 mg twice daily and glyburide 10 mg twice daily. He recently began measuring his preprandial blood glucose level; his home blood glucose profile for the past week is as follows:

He follows a reasonable meal plan with consistent carbohydrate intake at each meal. His exercise routine is to walk for 20 minutes three times per week. Relevant laboratory data are a hemoglobin A1c value of 9.4% and a serum creatinine concentration of 1.8 mg/dL (159.16 µmol/L). Results of liver function tests are normal.

To lower glucose levels to an acceptable target in this patient, which of the following is the most appropriate adjustment of his treatment regimen?

A. Continue metformin and glyburide, and start basal insulin at night.

B. Continue metformin and glyburide, and start 70/30 premixed insulin before supper.

D. Stop metformin and glyburide, and start 70/30 premixed insulin twice daily.