How does cholestyramine work in the body?
Cholestyramine is a bile-acid sequestrant. It acts in the gut by binding bile acids (specifically in the intestine) and preventing their reabsorption back into the bloodstream. With fewer bile acids being re-circulated, the liver pulls more cholesterol from the blood to make new bile acids, which lowers circulating cholesterol levels.
Why does binding bile acids lower cholesterol?
By interrupting enterohepatic circulation (the normal recycling of bile acids from the intestine back to the liver), cholestyramine reduces the bile-acid pool returning to the liver. The liver responds by increasing conversion of cholesterol into bile acids. This increased use of cholesterol leads to reduced serum cholesterol.
What does cholestyramine do for bile-acid–related diarrhea?
When bile acids reach the colon in higher-than-normal amounts, they can stimulate water and electrolyte secretion, causing diarrhea (commonly described as bile-acid diarrhea). Cholestyramine binds bile acids in the intestinal lumen, so fewer bile acids irritate the colon lining and the secretory effect is reduced, improving diarrhea.
Does cholestyramine get absorbed systemically?
No. Cholestyramine works locally in the gastrointestinal tract by binding substances in the intestinal contents. Because it is not absorbed in a clinically meaningful way, its main actions are in the gut rather than through systemic receptor effects.
Mechanism-related practical point: drug and nutrient absorption
Since cholestyramine binds substances in the gut, it can reduce absorption of other oral drugs if they are taken at the same time. Separating doses from other medications is a common clinical approach to avoid unintended reductions in drug exposure.
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