Development and validation of an LC–MS/MS method for the determination of quetiapine and four related metabolites in human plasma

Pharmacokinetic measurement of the psychotropic compound quetiapine and four related metabolites in human plasma was conducted using a sensitive and specific liquid–chromatography tandem mass spectrometry (LC–MS/MS) assay that has been developed and validated for this purpose. The assay employs a single liquid–liquid extraction of quetiapine and its N-desalkyl (norquetiapine, M211,803, M1), 7-hydroxy (M214,227, M2), 7-hydroxy N-desalkyl (M236,303, M3), and sulfoxide (M213,841, M4) metabolites from human plasma, and utilizes dual-column separation, using Luna C18 columns (50 mm × 2.0 mm, 5 μm) and positive ionization tandem MS detection in the multiple reaction monitoring (MRM) mode of the analytes and their respective stable labeled internal standards. The method provides a linear response from a quantitation range of <0.70 ng/ml to at least 500 ng/ml for each analyte using 40 μl of plasma. The applicable range was extended by dilution up to 100-fold with blank matrix. The accuracy and precision for quetiapine were less than 6.0% and 6.4% for quetiapine, respectively. The accuracy (and precision) was less than 9.4% (5.9%) for norquetiapine; 6.4% (6.2%) for M2; and 10.0% (6.4%) for M3; and 8.6% (9.5%) for M4. This methodology enabled the determination of the pharmacokinetics of quetiapine and its metabolites in human plasma, and an example of its application is presented.