Professional and Linguistic Assessments Board (PLAB) Practice Exam

What is the mechanism of action of sitagliptin?

1. DPP-4 inhibitor

2. GLP-1 analog

3. Insulin sensitizer

4. Beta-blocker

The correct answer is: DPP-4 inhibitor

Sitagliptin is classified as a DPP-4 inhibitor, which stands for dipeptidyl peptidase-4. Its primary mechanism of action involves the inhibition of the DPP-4 enzyme, which is responsible for the breakdown of incretin hormones, particularly GLP-1 (glucagon-like peptide-1) and GIP (gastric inhibitory polypeptide). By inhibiting this enzyme, sitagliptin increases the levels of active incretin hormones in the body. The elevation of these incretin hormones enhances insulin secretion from the pancreas in response to meals and reduces glucagon levels, which in turn helps to lower blood glucose levels. This makes sitagliptin an effective treatment for type 2 diabetes, as it works to improve glycemic control without causing significant weight gain or increasing the risk of hypoglycemia, which can be concerns with other antidiabetic medications. The other options represent different classes of medications that operate through distinct mechanisms. For instance, GLP-1 analogs mimic the effects of GLP-1 but do so through a different mechanism than DPP-4 inhibitors. Insulin sensitizers improve the body's response to insulin but do not involve the incretin pathway directly.