Clozapine and norclozapine monitoring in plasma following surfactant assisted dispersive liquid-liquid microextraction

Clozapine is the drug of choice for treatment-resistant schizophrenia. However, it is characterized by inter- and intraindividual variability in plasma concentrations and complex metabolism requiring drug monitoring. A surfactant-assisted dispersive liquid-liquid microextraction method followed by high-performance liquid chromatography-ultraviolet is proposed to determine clozapine and its primary active metabolite, norclozapine, in plasma using haloperidol (400 ng/mL) as an internal standard. The surfactant, cetyl trimethyl ammonium bromide (0.5 mmol/L), and 1-octanol (extraction solvent) were rapidly injected into the diluted plasma to form a cloudy solution. After centrifugation, 50 mu L of the organic phase was injected into high-performance liquid chromatography for analysis. The procedure was optimized by controlling the extraction solvent type and volume, the surfactant type and concentration, pH, and ionic strength. Furthermore, its suitability was investigated using plasma samples obtained from two healthy volunteers following a 12.5 mg dose of clozapine. The analytical performance of the method was acceptable with a limit of quantification of 0.9 and 0.4 ng/mL for clozapine and norclozapine, respectively (r(2) > 0.999) and a wide linear dynamic range 6.25-1600 ng/mL. The optimized method is simple, practical, environmentally friendly, and economically acceptable. It also requires a small amount of the sample.