Metabolism of ursodeoxycholic acid in human raises challenges to its bioequivalence studies

Ursodeoxycholic acid (UDCA) is an essential drug for the treatment of cholestatic liver diseases. As the most important representative of endogenous drugs, the metabolism and disposition of UDCA in human is characterized by both host-gut microbial co-metabolism and hepato-billilary-intestinal circulation. These distinct metabolic and pharmacokinetic features have brought great challenges into the bioequivalence (BE) evaluation of UDCA generic formulations. These challenges include not only biopharmaceutical problems derived from the unique physiochemical properties of amphiphilic molecules and the large single dose, but also the drug metabolism and pharmacokinetic problems associated with endogenous metabolism, long terminal half-life, high inter-and intra-individual variations, as well as accurate determination of UDCA and its metabolites. This review summarized academic and industrial literatures about the clinical pharmacokinetics and endogenous metabolism of UDCA. Current guidelines and technical challenges of UDCA BE studies were extensively discussed. Knowledge summarized in this review is expected to provide valuable reference for the development of UDCA generic formulations.