In vitro studies using rat, mouse, and human microsomes and hepatocytes on the bacterial β-glucuronidase inhibitor 1-((6,8-dimethyl-2-oxo-1,2-dihydroquinolin-3-yl)methyl)-3-(4-ethoxyphenyl)-1-(2-hydroxyethyl)thiourea) (Inh 1) revealed extensive metabolism in all species.The intrinsic clearances of Inh 1 in human, mouse, and rat hepatic microsomes were 30.9, 67.8, and 201 µL/min/mg, respectively. For intact hepatocytes intrinsic clearances of 21.6, 96.0, and 129 µL/min/106 cells were seen for human, mouse and rat, respectively.The metabolism of Inh 1 involved an uncommon desulphurisation reaction in addition to oxidation, deethylation, and conjugation reactions at multiple sites. Six metabolites were detected in microsomal incubations in human and rat, and seven for the mouse. With hepatocytes, 18 metabolites were characterised, 9 for human, and 11 for mouse and rat.Following IV administration to mice (3 mg/kg), plasma concentrations of Inh 1 exhibited a monophasic decline with a terminal elimination half-life of 0.91 h and low systemic clearance (11.8% of liver blood flow). After PO dosing to mice (3 mg/kg), peak observed Inh 1 concentrations of 495 ng/mL were measured 0.5 h post dose, declining to under 10 ng/mL at 8 h post dose. The absolute oral bioavailability of Inh 1 in the mouse was ca. 26%.
