A sensitive method for the determination of the novel cholinesterase inhibitor ZT-1 and its active metabolite huperzine A in rat blood using liquid chromatography/tandem mass spectrometry.

ZT-1 has been developed as a novel acetylcholinesterase inhibitor, but is rapidly degraded to huperzine A (Hup A) in water or aqueous organic solvents. A sensitive method has been developed for simultaneous determination of ZT-1 and its active metabolite Hup A in blood, and was applied to the investigation of the pharmacokinetics of ZT-1 in rats. The method involves immediate hydrogenation of ZT-1 with sodium borohydride to the stable form rZT-1 following blood sampling. The NaBH4-treated blood sample is then submitted to liquid-liquid extraction, and the resultant extract is analyzed by liquid chromatography with electrospray ionization and tandem mass spectrometry. Huperzine B is used as internal standard for the quantification. ZT-1 was found to be rapidly absorbed in the intestinal tract, with a time to reach the peak blood concentration (Tpeak) of 5 min after an intragastric dose of ZT-1 embedded in povidone to rats at 0.5 mg ZT-1/kg. The mean maximum blood concentration (Cmax) and area under the blood level-time curve (AUC(0 --> 8)) of ZT-1 were 1.57 ng/mL and 0.48 ng. h/mL, respectively. The Tpeak, Cmax, and AUC values of the metabolite Hup A were 0.22 h, 109.9 ng/mL, and 96.3 ng. h/mL, respectively. Following an intravenous dose of 0.1 mg ZT-1/kg rat body weight, the blood concentration of ZT-1 was higher than that of Hup A, and the AUC(0 --> 8) values were 26.2 ng. h/mL for ZT-1 and 6.0 ng. h/mL for Hup A. The elimination half-lives (T1/2) of ZT-1 and Hup A were 0.68 and 1.47 h, respectively. The oral bioavailability (F) of intact ZT-1 in rats treated with ZT-1 embedded in povidone was very low, 0.37%. Copyright 2004 John Wiley & Sons, Ltd.