Separation and quantitation of cis- and trans-thiothixene in human plasma by high-performance liquid chromatography.

A high-performance liquid chromatographic procedure is described for the separation of cis and trans isomers of thiothixene, a thioxanthene derivative used as an antipsychotic agent. A radial compression module (RCM-100) was used with both silica and cyanopropyl cartridges. A fixed-wavelength UV detector (254 nm) was used in these studies for quantitation. Mesoridazine is used as an internal standard because of its separation characteristics and reproducible quantitation. C18 Sep-Pak cartridges are used for biological sample clean-up. Plasma samples from patients treated with thiothixene (Navane) were assayed for cis and trans-thiothixene. No trans-thiothixene was detectable and cis-thiothixene concentrations ranged from 0 to 22.5 ng/ml.