TY - JOUR T1 - Analysis of phase I and phase II metabolites of tamoxifen in breast cancer patients. JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 1119 LP - 1124 VL - 21 IS - 6 AU - G K Poon AU - Y C Chui AU - R McCague AU - P E Lłnning AU - R Feng AU - M G Rowlands AU - M Jarman Y1 - 1993/11/01 UR - http://dmd.aspetjournals.org/content/21/6/1119.abstract N2 - This study describes the application of LC/MS/MS to the determination of phase I and phase II metabolites of tamoxifen in urine and plasma samples of breast cancer patients. In the plasma extracts, in addition to the parent drug and N-desmethyltamoxifen, a minor metabolite tamoxifen N-oxide was identified for the first time in human. Four intact glucuronides of tamoxifen metabolites were isolated in the 24-hr posttreatment urine sample. They were the glucuronides of 4-hydroxytamoxifen, 4-hydroxy-N-desmethyltamoxifen, dihydroxytamoxifen, and a monohydroxy-N-desmethyltamoxifen. Hydroxylation followed by glucuronidation is a well-established metabolic route of tamoxifen, and this study describes for the first time direct analyses of these metabolites in human urine samples using on-line LC tandem MS. ER -