Clinical pharmacokinetics of therapeutic bile acids.

The pharmacokinetics of chenodeoxycholic and ursodeoxycholic acids are reviewed in this article. Chenodeoxycholic acid is well absorbed by the intestine, whereas the absorption of ursodeoxycholic acid is incomplete. They are extracted efficiently by the liver, conjugated with glycerine and taurine, secreted in bile, and then undergo enterohepatic circulation with the endogenous bile acids. Therapeutic bile acids are metabolised by intestinal bacteria to lithocholic acid which is mainly excreted with faeces. Since the large majority of bile acid is confined within the enterohepatic circulation (resulting in low serum concentrations) their volume of distribution is relatively high. Despite the high hepatic extraction, the clearance of therapeutic bile acids is relatively low because of the highly efficient enterohepatic recirculation. Elimination of therapeutic bile acids mainly occurs in the faeces either unmodified or after biotransformation. At present the main clinical indication for therapeutic bile acids is ursodeoxycholic acid treatment for chronic cholestatic liver disease. In these patients, ursodeoxycholic acid is efficiently absorbed but its hepatic uptake and biliary secretion are impaired, thus leading to reduced biliary enrichment and high serum concentrations of this exogenous bile acid. In patients with cystic fibrosis-associated liver disease, bile acid malabsorption also occurs, thus indicating the need for higher dosages. The volume of distribution and clearance of ursodeoxycholic acid reduced in the presence of liver disease. Also in this case, elimination mainly occurs with the faeces but, in the presence of severe cholestasis, renal clearance may become relevant. Sulphation or conjugation with glucose and N-acetylglucosamine facilitate urinary excretion.