Observation of Clinically Relevant Drug Interaction in Chimeric Mice with Humanized Livers: The Case of Valproic Acid and Carbapenem Antibiotics.

Human in vitro and dog in vitro/in vivo researches indicate that the drug-drug interaction (DDI) of decreased plasma valproic acid (VPA) concentration by co-administration of carbapenem antibiotics is caused by inhibition of acylpeptide hydrolase (APEH)-mediated VPA acylglucuronide (VPA-G) hydrolysis by carbapenems. In this study, we investigated VPA disposition and APEH activities in TK-NOG chimeric mice, whose livers were highly replaced with human hepatocytes, to evaluate the utility of this animal model and the clinical relevance of the DDI mechanism. VPA and VPA-G concentrations in plasma, urinary excretion of VPA-G and APEH activity in humanized livers were measured after co-administration of VPA with meropenem (MEPM) to chimeric mice. After co-administration with MEPM to the chimeric mice, plasma VPA concentration more rapidly decreased than without the co-administration. An increase in plasma AUC and urinary excretion of VPA-G was also observed. APEH activity in humanized livers was strongly inhibited even at 24 h after co-administration of MEPM to the chimeric mice. The DDI of VPA with carbapenems was successfully observed in chimeric mice with humanized livers. The DDI was caused by long-lasting inhibition of hepatic APEH-mediated VPA-G hydrolysis by carbapenems, which strongly supports the APEH-mediated mechanism of the clinical DDI. This is the first example showing the usefulness of chimeric mice with humanized livers for evaluation of a DDI via non-cytochrome P450 enzyme.