Development of a novel tandem mass spectrometry method for the quantification of eszopiclone without interference from 2-amino-5-chloropyridine and application in a pharmacokinetic study of rat.

• Illuminated the instability and controllability of eszopiclone (E-ZOP) in biological matrices because of the hydrolysis at different pH points. • Simplified the method of extraction of E-ZOP from biological matrices, liquid-liquid or solid phase extraction was replaced by direct protein precipitation with acetonitrile. • Monitored hydrolysis production via 2-amino-5-chloropyridine (ACP) throughout the whole HPLC-MS/MS method validation for quantified E-ZOP in rat plasma. • Developed and validated the simple, precise and sensitive HPLC–MS/MS method and successfully applied the method to the determination of E-ZOP in rat plasma. Eszopiclone (E-ZOP), a strictly controlled psychoactive drug, must be accurately quantified in biological matrices. However, because of its rapid degradation and transformation into 2-amino-5-chloropyridine (ACP) during specimen preparation, the concentration of E-ZOP in biological matrices is likely underestimated. In this study, a sensitive and simple high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method for the accurate determination of the initial concentration of E-ZOP in rat plasma was developed and validated. ACP was monitored simultaneously throughout the method validation process to ensure that it was not produced via E-ZOP hydrolysis. E-ZOP and structurally similar metabolites were stabilized in rat plasma by controlling the pH at 4.2 using a modified phosphate buffer solution (PBS) with acetic acid. Using this method, E-ZOP, ACP and the internal standard (IS), venlafaxine, were extracted from rat plasma via a simple protein precipitation and separated on a C 18 column using methanol, 5 mM ammonium acetate, and 0.1 % acetic acid as the isocratic mobile phase. The validated method covered a working range from 0.1–50 ng/mL for E-ZOP, and the lower limit of detection (LLOD) for ACP was 0.2 ng/mL. In conclusion, an accurate, sensitive, and simple HPLC-MS/MS method for E-ZOP quantification was developed and successfully applied to a preclinical pharmacokinetics (PK) study in rats. The toxic product APC was effectively monitored. The HPLC-MS/MS method is a stable and sensitive quantitative method for the determination of E-ZOP in biological matrices. [ABSTRACT FROM AUTHOR]