Which of the following is NOT an anti-hyperlipidemic agent?

Metformin is not classified as an anti-hyperlipidemic agent; it is primarily used as an antihyperglycemic medication to manage type 2 diabetes. Metformin works by decreasing hepatic glucose production and improving insulin sensitivity, leading to better blood sugar control. While metabolic syndrome and diabetes can often be associated with lipid abnormalities, metformin itself does not directly target lipid levels.

In contrast, atorvastatin and simvastatin are both statins, which are a class of drugs specifically designed to lower cholesterol levels by inhibiting HMG-CoA reductase, an enzyme involved in cholesterol synthesis in the liver. Cholestyramine, on the other hand, is a bile acid sequestrant. It lowers cholesterol levels by binding bile acids in the intestine, resulting in their excretion and forcing the liver to utilize cholesterol to replace the lost bile acids, thereby reducing serum cholesterol levels.

Given this information, metformin stands apart from the other choices, as its primary use is for glucose management, not for addressing hyperlipidemia.