Final answer:
Exenatide (Byetta®) is the medication contraindicated in gastroparesis among the options provided, because it slows gastric emptying which could exacerbate gastroparesis symptoms.
Step-by-step explanation:
Gastroparesis is a condition that affects the stomach muscles and prevents proper stomach emptying. Among the drugs used to treat type 2 diabetes mellitus, exenatide (Byetta®) is contraindicated in gastroparesis because it slows gastric emptying, which can worsen the symptoms of this condition. Exenatide belongs to a class of medications known as incretin mimetics, which enhance insulin secretion in response to meals, but this mechanism can be problematic for patients with gastroparesis.
On the other hand, drugs such as pioglitazone (Actos®), sitagliptin (Januvia®), and sulfonylureas like glyburide (Glynase®) do not directly affect stomach emptying and are not typically contraindicated in gastroparesis in the same way as exenatide.