%0 Journal Article %A ELTON RICHARD KISANGA %A GUNNAR MELLGREN %A ERNST A. LIEN %T Excretion of Hydroxylated Metabolites of Tamoxifen in Human Bile and Urine %D 2005 %J Anticancer Research %P 4487-4492 %V 25 %N 6C %X The selective oestrogen-receptor modulator tamoxifen is the most commonly used drug against breast cancer. It has potent metabolites, such as 4-hydroxytamoxifen. Recently, the metabolite 4-hydroxy-N-desmethyltamoxifen has received increased attention as it may be a major contributor to the overall effects of tamoxifen. The excretion of tamoxifen and its metabolites was examined in a patient with biliary drainage after an oral dose of [14C]tamoxifen. During the first 10 days after oral dosing, 11.5, 26.7 and 24.7% of the radioactivity was excreted in the bile, urine and faeces, respectively. After deconjugation with beta-glucuronidase, the concentrations of tamoxifen and 4 of its metabolites were measured, and it was observed that the hydroxylated metabolites were excreted in the bile and urine. 4-Hydroxytamoxifen was the dominant compound, being detected during the first day of observation, whereas 4-hydroxy-N-desmethyltamoxifen was first observed in the urine and bile after 4 days. This is the first report on tamoxifen excretion in human bile and urine demonstrating that 4-hydroxytamoxifen may be a first-pass metabolite. In contrast, the potent metabolite 4-hydroxy-N-desmethyltamoxifen was first detected 4 days after administration of a single oral dose. Copyright© 2005 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved %U https://ar.iiarjournals.org/content/anticanres/25/6C/4487.full.pdf