Here's a recent thread:
UDCA dosage vs tudca dosage
Also, there's this:
The mechanism of action of udca in liver and cholestatic disorders has not yet been explained totally. However, udca alters bile acid composition, resulting in increases in the concentration of udca and decreases in the concentrations of the more hydrophobic and potentially toxic bile acids, cholic and chenodeoxycholic acids. udca also has a choleretic effect, resulting in increased bile acid output and bile flow. There is some evidence for immunological effects, including a reduction of abnormal expression of HLA Class I antigens on hepatocytes and a suppression of immunoglobulin and cytokine production.
udca occurs naturally in the body. After oral administration of a single 500 mg dose of udca to healthy volunteers, peak plasma concentrations were 7 to 16 µM. Tmax occurs at 60 minutes and a second peak plasma concentration occurs at 180 minutes. After oral administration of 250 mg, 500 mg, 1000 mg and 2000 mg single doses, respective absorption rates were 60.3%, 47.7%, 30.7% and 20.7% based on recovery from bile within 24 hours in patients with external biliary drainage.
In plasma, protein binding is 96 - 98%.
First pass extraction of udca from the portal vein by the liver ranges from 50 - 70%. udca is conjugated to glycine and taurine and then excreted into bile and passes to the small bowel. In the intestine, some conjugates are deconjugated and reabsorbed in the terminal ileum. Conjugates may also be dehydroxylated to lithocholic acid, part of which is absorbed, sulphated by the liver and excreted by the biliary tract. In healthy volunteers given udca 500 mg with 14C tracer, 30 - 44% of the dose was excreted in faeces in the first three days as udca (2 - 4%), lithocholic acid (37%) and 7-ketolithocholic acid (5%).
The biological half-life of orally administered udca is 3.5 - 5.8 days."