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Ursodiol is a naturally-occurring bile acid that is made by the liver in humans and is secreted in small quantities into bile . It is used to dissolve and prevent cholesterol gallstones and to treat primary biliary cirrhosis , a disease of the liver. Ursodiol blocks the enzyme in the liver that produces cholesterol and thereby decreases production of cholesterol by the liver and the amount of cholesterol in bile. It also reduces the absorption of cholesterol from the intestine. By decreasing the concentration of cholesterol in bile, ursodiol prevents the formation and promotes the dissolution of cholesterol-containing gallstones. The mechanism by which it acts in primary biliary cirrhosis is not clear. The FDA approved ursodiol in December 1987.
In 103-week oral carcinogenicity studies of lithocholic acid, a metabolite of Ursodiol, doses up to 250 mg/kg/day in mice and 500 mg/kg/day in rats did not produce any tumors. In a 78-week rat study, intrarectal instillation of lithocholic acid (1 mg/kg/day) for 13 months did not produce colorectal tumors. A tumor-promoting effect was observed when it was administered after a single intrarectal dose of a known carcinogen N-methyl-N'-nitro-N-nitrosoguanidine. On the other hand, in a 32-week rat study, Ursodiol at a daily dose of 240 mg/kg (1,440 mg/m 2 , times the maximum recommended human dose based on body surface area) suppressed the colonic carcinogenic effect of another known carcinogen azoxymethane.