Analysis of LK-157 in Plasma by LC–MS–MS: Application to Studies of Pharmacokinetics and Degradation Pathways in Rats and Dogs

Multiple-species plasma-stability testing and pharmacokinetic studies in rats and dogs were performed on LK-157, a novel 10-ethylidene tricyclic carbapenem and potent inactivator of β-lactamases of classes A, C, and D. An LC–MS–MS method was developed and validated for analysis of LK-157 in rat and dog plasma. Separation was achieved on a C₁₈ column by gradient elution. The lower limit of quantification for LK-157 in plasma was 50 ng mL^?1. Intra-day and inter-day precision were <12.5 and <11.8%, respectively. When degradation of LK-157 was assessed in buffer solutions and in rat, dog, and human plasma, the compound was found to be stable in pH 7.0–9.0 phosphate buffer for 24 h at room temperature, and in human plasma for 60 min at 37 °C. The stability of LK-157 was species-dependent. Results from study of in vitro metabolism showed that the enzymes liver cytochrome P450 and uridine diphosphate glycosyltransferase do not metabolize LK-157. LC–MS–MS was also successfully applied to a pharmacokinetic study. The pharmacokinetics of LK-157 after bolus intravenous administration (10 mg kg^?1) to Wistar rats and Beagle dogs was described by a two-compartment pharmacokinetic model. Human pharmacokinetic data were extrapolated from dog pharmacokinetic data. The extrapolated human terminal-phase half-life of LK-157 was 2.3 h. Stability and pharmacokinetic data for LK-157 are in agreement with results for other inactivators of β-lactamases.