An overweight 48-year-old male presents with complaints of increased thirst and frequent urination. Laboratory examination reveals a blood glucose level of 180 mg/dL. The patient's past medical history is unremarkable, except for an anaphylactic reaction that occurred one year ago when he was given trimethoprim-sulfamethoxazole for a sinus infection. Based on this information, which of the following agents should be prescribed?

The patient's initial presentation strongly suggests Type 2 diabetes mellitus (NIDDM), which usually begins in middle or late life. Symptoms often develop gradually, and the diagnosis is frequently made when an asymptomatic or mildly symptomatic patient is found on routine laboratory examination to have an elevated blood glucose level. Therapy with an oral hypoglycemic agent would be appropriate in this case. Since the patient had a documented anaphylactic reaction to trimethoprim-sulfamethoxazole, he should not take any "sulfa" drugs, including the sulfonylurea type oral hypoglycemic agents such as chlorpropamide and glipizide. Metformin is a biguanide oral hypoglycemic agent, chemically distinct from the sulfonylureas. This medication is indicated as monotherapy or in conjunction with other oral hypoglycemic agents in the treatment of NIDDM. Glucagon is the drug of choice for the treatment of severe hypoglycemia; this agent would worsen the patient's hyperglycemia.