title: Quantification of tamoxifen and three of its phase-I metabolites in human plasma by liquid chromatography/triple-quadrupole mass spectrometry.
abstract: In view of future pharmacokinetic studies, a highly sensitive ultra performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) method has been developed for the simultaneous quantification of tamoxifen and three of its main phase I metabolites in human lithium heparinized plasma. The analytical method has been thoroughly validated in agreement with FDA recommendations. Plasma samples of 200 μl were purified by liquid-liquid extraction with 1 ml n-hexane/isopropanol, after deproteination through addition of 50 μl acetone and 50 μl deuterated internal standards in acetonitrile. Tamoxifen, N-desmethyl-tamoxifen, 4-hydroxy-tamoxifen and endoxifen were chromatographically separated on an Acquity UPLC(®) BEH C18 1.7 μm 2.1 mm×100 mm column eluted at a flow-rate of 0.300 ml/min on a gradient of 0.2mM ammonium formate and acetonitrile, both acidified with 0.1% formic acid. The overall run time of the method was 10 min, with elution times of 2.9, 3.0, 4.1 and 4.2 min for endoxifen, 4-hydroxy-tamoxifen, N-desmethyl-tamoxifen and tamoxifen, respectively. Tamoxifen and its metabolites were quantified by triple-quadrupole mass spectrometry in the positive ion electrospray ionization mode. The multiple reaction monitoring transitions were set at 372>72 (m/z) for tamoxifen, 358>58 (m/z) for N-desmethyl-tamoxifen, 388>72 (m/z) for 4-hydroxy-tamoxifen and 374>58 (m/z) for endoxifen. The analytical method was highly sensitive with the lower limit of quantification validated at 5.00 nM for tamoxifen and N-desmethyl-tamoxifen and 0.500 nM for 4-hydroxy-tamoxifen and endoxifen, which is equivalent to 1.86, 1.78, 0.194 and 0.187 ng/ml for tamoxifen, N-desmethyl-tamoxifen, 4-hydroxy-tamoxifen and endoxifen, respectively. The method was also precise and accurate, with within-run and between-run precisions within 12.0% and accuracy ranging from 89.5 to 105.3%. The method has been applied to samples from a clinical study and cross-validated with a validated LC-MS/MS method in serum.
authors.affiliation: Department of Hospital Pharmacy, Erasmus MC, University Medical Center, Rotterdam, The Netherlands.
authors.forename: Lisette
authors.initials: L
authors.lastname: Binkhorst
authors.forename: Ron H J
authors.initials: RH
authors.lastname: Mathijssen
authors.forename: Inge M
authors.initials: IM
authors.lastname: Ghobadi Moghaddam-Helmantel
authors.forename: Peter
authors.initials: P
authors.lastname: de Bruijn
authors.forename: Teun
authors.initials: T
authors.lastname: van Gelder
authors.forename: Erik A C
authors.initials: EA
authors.lastname: Wiemer
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Loos
mesh_terms: D002138:Calibration; D002853:Chromatography, Liquid / Q000379:methods*; D006801:Humans; D012015:Reference Standards; D015203:Reproducibility of Results; D020845:Selective Estrogen Receptor Modulators / Q000097:blood* / Q000493:pharmacokinetics; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013629:Tamoxifen / Q000097:blood* / Q000493:pharmacokinetics
chemical_list: D020845:Selective Estrogen Receptor Modulators; D013629:Tamoxifen