ANTIHYPERLIPIDAEMIC AGENTS (lipid-lowering drugs, antihypercholesterolaemic agents, lipid-regulating drugs) are used in clinical conditions of hyperlipidaemia, where there are very high levels of the lipids cholesterol and/or triglycerides in the blood plasma, and more generally in the treatment of coronary heart disease. Medical evidence suggests that if diet or drugs can be used to lower levels of LDL-cholesterol (low-density lipoprotein), whilst raising HDL-cholesterol (high-density lipoprotein), then there may be a regression of the progress of coronary atherosclerosis — a diseased state of the arteries of the heart where plaques of lipid material narrow blood vessels, which contributes to angina pectoris attacks, and to the formation of abnormal clots which go on to cause heart attacks and strokes. The initial use of lipid-lowering drugs was mainly only in familial hyperlipidaemia, or where distinct clinical signs indicate the need for intervention. In most individuals an appropriate type of low fat diet can adequately do what is required, but the agents are now used more in treating a range of cardiovascular diseases. Lipid-lowering drugs work in several ways.

The polymeric ion-exchange resins cholestyramine and colestipol act by binding bile acids, preventing their reabsorption; so promoting hepatic conversion of cholesterol into bile acids. This results in increased LDL-receptor activity of liver cells, which increases the break down of LDL-cholesterol. In this way the compounds effectively reduce LDL-cholesterol (but can aggravate hypertriglyceridaemia).

The clofibrate group of drugs (bezafibrate, ciprofibrate, clofibrate, fenofibrate, gemfibrozil are in use) reduce triglycerides, reduce LDL-cholesterol and raise HDL-cholesterol.

Simvastatin, pravastatin and fluvastatin have been recently introduced into clinical use. Of fungal origin, they inhibit an enzyme in the liver — HMG-CoA reductase — with the end result that LDL-cholesterol is better cleared from the body. See HMG-COA REDUCTASE INHIBITORS.

The nicotinic acid group (acipimox, nicotinic acid) can lower cholesterol and triglyceride levels by an action on enzymes in the liver. The fish oils (e.g. omega-3 marine triglycerides) are dietary supplements that may be useful in treating hypertriglyceridaemia. Probucol can decrease both LDL-cholesterol and HDL-cholesterol, as well as having other beneficial properties.