title: Stereoselective measurement of E- and Z-doxepin and its N-desmethyl and hydroxylated metabolites by gas chromatography-mass spectrometry.
abstract: A stereoselective method of analysis of the antidepressant drug doxepin (DOX, an 85:15% mixture of E-Z stereoisomers), its principal metabolites E- and Z-N-desmethyldoxepin (desDOX) and ring-hydroxylated metabolites in microsomal incubation mixtures is described. DOX and its metabolites were extracted from alkalinised incubation mixtures by either: 9:1 hexane-propan-2-ol (method 1) or 1:1 hexane-dichloromethane (method 2), derivatised with trifluoroacetic anhydride and analysed by GC-MS with selected ion monitoring. Both methods were suitable for the analysis of individual desDOX isomers as indicated by correlation coefficients of > or = 0.999 for calibration curves constructed between 50 and 2500 nM, and good within-day precision at 125 nM (C.V. < or = 14%) and 1000 nM (C.V. < or = 8%). Method 1, however, was unsuitable for the analysis of ring-hydroxylated metabolites of DOX, whereas the hydroxylated metabolites of E-DOX and E-desDOX (generated in situ) were extracted by method 2 with a C.V. of ca. 13%. This is the first assay method that permits the simultaneous measurement of desDOX and hydroxylated metabolites of DOX in microsomal mixtures.
authors.affiliation: Key Centre for Applied and Nutritional Toxicology, RMIT University, Melbourne, Victoria, Australia. v.haritos@ento.csiro.au
authors.forename: V S
authors.initials: VS
authors.lastname: Haritos
authors.forename: H
authors.initials: H
authors.lastname: Ghabrial
authors.forename: J T
authors.initials: JT
authors.lastname: Ahokas
authors.forename: M S
authors.initials: MS
authors.lastname: Ching
mesh_terms: D000929:Antidepressive Agents, Tricyclic / Q000032:analysis*; D002138:Calibration; D004316:Doxepin / Q000031:analogs & derivatives / Q000032:analysis* / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods* / Q000592:standards; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006900:Hydroxylation; D008862:Microsomes, Liver / Q000737:chemistry / Q000378:metabolism; D009661:Nortriptyline; D012680:Sensitivity and Specificity; D013237:Stereoisomerism
chemical_list: D000929:Antidepressive Agents, Tricyclic; D004316:Doxepin; D009661:Nortriptyline; C028701:desmethyldoxepin