A method for rapid determination of zotepine by gas chromatography-mass spectrometry

A rapid and sensitive method using solid-phase extraction and gas chromatography-mass spectrometry (GC-MS) has been developed for the determination of zotepine (ZTP), an atypical neuroleptic, in human plasma. The detection limit of ZTP was 1 microgram/L. Standard curves over the concentration range from 2.5 to 100 micrograms/L had a good linearity. Intraassay variability ranged from 2.2 to 3.3% and interassay variability from 3.5 to 6.6% at the concentration range of 5-75 micrograms/L. Our preliminary data of single-dose kinetics of ZTP by using this method suggested that the peak time and elimination half-life was much longer than previously reported, and that there appeared to be a second peak after 10-12 h of ZTP administration, indicating the possibility of the presence of enterohepatic recirculation.