All of the following antidiabetic drugs act by enhancing insulin resistance except
**Question:** All of the following antidiabetic drugs act by enhancing insulin resistance except
A. Metformin
B. Sulfonylureas
C. Thiazolidinediones
D. Glucagon-like peptide-1 (GLP-1) receptor agonists
**Core Concept:**
Insulin resistance is a key feature in the pathogenesis of type 2 diabetes mellitus (T2DM). Antidiabetic drugs are classified into various categories based on their mode of action, which can be grouped into insulin sensitizers (enhancing insulin sensitivity) and insulin secretagogues (stimulating insulin secretion). Insulin sensitizers are further subdivided into sulfonylureas, thiazolidinediones, and GLP-1 receptor agonists. Sulfonylureas directly stimulate insulin secretion, while GLP-1 receptor agonists improve insulin sensitivity by acting on the GLP-1 receptor in the pancreas. Thiazolidinediones are insulin sensitizers that act by improving insulin sensitivity through binding to and activating the peroxisome proliferator-activated receptor gamma (PPAR-Ξ³).
**Why the Correct Answer is Right:**
Metformin is a biguanide, a class of antidiabetic drugs that primarily act by reducing hepatic glucose production. It does not act by enhancing insulin resistance or improving insulin sensitivity. Instead, metformin lowers blood glucose levels by decreasing hepatic glucose production, increasing muscle glucose uptake, and improving insulin sensitivity in peripheral tissues.
**Why Each Wrong Option is Incorrect:**
A. Sulfonylureas (e.g., Glyburide) act by directly stimulating insulin secretion from beta cells of the pancreas. They are not involved in enhancing insulin resistance.
B. Thiazolidinediones (e.g., Pioglitazone) improve insulin sensitivity by binding to and activating the PPAR-Ξ³ (peroxisome proliferator-activated receptor gamma) in adipose tissue, skeletal muscle, and liver. They do not involve enhancing insulin resistance either.
C. GLP-1 receptor agonists (e.g., Liraglutide) act by mimicking the effects of glucagon-like peptide-1 (GLP-1), a gastrointestinal hormone that enhances insulin secretion and suppresses glucagon secretion in a glucose-dependent manner. GLP-1 receptor agonists improve glucose control by enhancing insulin secretion and inhibiting glucagon secretion without enhancing insulin resistance.
D. Glucagon-like peptide-1 (GLP-1) is an incretin hormone that enhances insulin secretion in a glucose-dependent manner and inhibits glucagon secretion. GLP-1 receptor agonists mimic the effects of GLP-1, improving glucose control and decreasing HbA1c levels in patients with T2DM. They do not increase insulin resistance.
**Why the Wrong Options Are Incorrect:**
A. Sulfonylureas like Glyburide directly stimulate insulin secretion from beta cells. They do not enhance insulin resistance.
B. Thiazolidinediones like Pioglitazone improve insulin sensitivity through PPAR-Ξ³ activation in adipose tissue, muscle, and liver, thereby