SIMULTANEOUS QUANTIFICATION OF TAMOXIFEN AND 4-HYDROXY-N-DESMETHYLTAMOXIFEN LEVELS IN HUMAN PLASMA BY LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY: DEVELOPMENT AND APPLICATION IN BREAST CANCER PATIENTS
Objective: This study was aimed to develop a highly sensitive and selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method
for the simultaneous quantification of tamoxifen, endoxifen, and clomiphene (internal standard) levels in human plasma.
Methods: Plasma samples from 40 patients with breast cancer were prepared through liquidâ€“liquid extraction in ethyl acetate, and chromatographic
separation was performed on an Acquity UPLC BEH C18 column (1.7 Î¼m, 2.1 mmÃ—100 mm). The sample was eluted within 6.50 min at a flow rate of
0.200 ml/min under a gradient of 0.2% formic acid and acetonitrile. The analytes were then quantified through triple quadrupole MS with electrospray
ionization in the positive ion mode and multiple reaction monitoring.
Results: The method was successfully used to quantify the plasma levels of tamoxifen and endoxifen, yielding respective measurement ranges
of 42.19â€“249.23 ng/ml and 1.52â€“26.62 ng/ml. Overall, this detection method was sensitive, with lower limits of quantitation of 0.625 ng/ml for
tamoxifen and 0.125 ng/ml for endoxifen. In addition, this method was precise and accurate, with a between-run variation range of 5.19â€“12.38% and
%diff range of âˆ’10.82%â€“+13.10%.
Conclusion: This method demonstrated that approximately 80% of patients had plasma levels of endoxifen exceeding the expected clinical threshold
(5.9 ng/ml). This rapid and simple method could be used to monitor tamoxifen metabolism and adjust doses as needed to achieve maximum
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