A 48-year-old woman who has had Type 2 diabetes mellitus for several years is seen for a routine follow-up evaluation. Her metabolic control has always been very good, with most hemoglobin A1c values less than 6.5%. Her current treatment is metformin 850 mg twice daily. She self-monitors her blood glucose two to three times daily and usually checks random 2-hour postprandial glucose values at least once daily. She notes that her postprandial glucose levels have been above her target of less than 160 mg/dL (8.88 mmol/L) for several weeks, despite increasing her activity level by walking three or four times weekly after dinner.

Her body mass index is 29.2. Her blood pressure is 128/86 mm Hg, and her A1c value is 7.2%. Self-monitored blood glucose values from the past week are noted in her log as follows:

Pre = preprandial; post = 2-hour postprandial.

Which of the following is the most appropriate change to this patient's treatment regimen?

A. Increase metformin to 1000 mg twice daily.

B. Initiate preprandial fast-acting insulin on nonexercise days. 

C. Add glargine at bedtime. 

D. Add a short-acting secretagogue (either repaglinide or nateglinide).