Colesevelam is a non-absorbed, lipid-lowering polymer that binds bile acids in the intestine, impeding their reabsorption. As the bile acid pool becomes depleted, the hepatic enzyme, cholesterol 7-(alpha)-hydroxylase, is upregulated, which increases the conversion of cholesterol to bile acids. This causes an increased demand for cholesterol in the liver cells, resulting in the dual effect of increasing transcription and activity of the cholesterol biosynthetic enzyme, hydroxymethyl-glutaryl-coenzyme A (HMG-CoA) reductase, and increasing the number of hepatic low-density lipoprotein (LDL) receptors. These compensatory effects result in increased clearance of LDL cholesterol (LDL-C) from the blood, resulting in decreased serum LDL-C levels. Serum triglyceride levels may increase or remain unchanged. The end result is increased clearance of LDL-cholesterol from the blood with decreased serum LDL-cholesterol.
Colesevelam is a high capacity bile-acid binding molecule. Colesevelam binds to bile acids in the intestine which reduces the amount of bile acids that are returned to the liver via enterohepatic circulation. Clinical studies have demonstrated that elevated levels of total cholesterol (total-C), LDL-C, and apolipoprotein B (Apo B, a protein associated with LDL-C) are associated with an increased risk of atherosclerosis in humans. Similarly, decreased levels of high-density lipoprotein cholesterol (HDL-C) are associated with the development of atherosclerosis. Epidemiological investigations have established that cardiovascular morbidity and mortality vary directly with the levels of total-C and LDL-C, and inversely with the level of HDL-C. The combination of colesevelam and an HMG-CoA reductase inhibitor is effective in further lowering serum total-C and LDL-C levels beyond that achieved by either agent alone.
Not applicable (not hydrolyzed by digestive enzymes and not absorbed).
Symptoms of overdose may include eye irritation, constipation, abdominal cramps, nausea, vomiting, diarrhea, and hypersensitivity. However, as colesevelam is not absorbed, the risk of systemic toxicity is low. Doses in excess of 4.5 g per day have not been tested.