Biliary excretion of warfarin metabolites and their metabolism by rat gut flora.

The bile was determined to be the major excretory route for ¹⁴C-warfarin in the rat with approximately 10% of the administered dose excreted within 5 hours after injection. Relatively little radioactivity appeared in the faces, indicating that considerable enterohepatic recycling was taking place. Less than 4% of the radioactivity in the bile could be extracted with organic solvents. Following incubation of the bile with β-glucuronidase or rat gut flora, however, the bulk of the radioactivity was extractable. The extent of gut flora-mediated hydrolysis of these polar biliary warfarin conjugates was approximately the same as obtained with β-glucuronidase. Approximately $\text{1}\text{3}$ of the gut flora-hydrolyzable conjugates were labile and subject to nonenzymatic hydrolysis at 37 C for 24 h. Chromatographic examination of the extracts from β-glucuronidase-treated bile revealed the presence of warfarin and 4′-, 6-, 7-, and 8-hydroxywarfarin. Warfarin and 7-hydroxywarfarin were the most abundant metabolites in the extracts.