Step 1: Understanding the Question:
We need to pick the oral anti-diabetic drug that works by blocking DPP-4, an enzyme that breaks down incretin hormones.
Step 2: Key Concept:
Drugs ending in "-gliptin" belong to the DPP-4 inhibitor class. DPP-4 normally degrades GLP-1 and GIP within minutes; stopping this enzyme keeps incretin levels high, which increases insulin release after meals.
Step 3: Detailed Explanation:
Metformin is a biguanide that reduces liver glucose output. Pioglitazone is a thiazolidinedione that improves insulin sensitivity through PPAR-gamma activation. Glipizide is a sulfonylurea that forces insulin release by blocking potassium channels on beta cells. None of these three touch DPP-4. Sitagliptin, by contrast, is named with the "-gliptin" suffix and is a direct DPP-4 inhibitor, matching the mechanism described in the question exactly.
Step 4: Final Answer:
The drug that raises incretin levels by inhibiting DPP-4 is Sitagliptin.