Abstract
Purpose: To compare serum and urine levels of tamoxifen and metabolites after a loading dose and at the steady state. Methods: A loading dose of 160 mg of tamoxifen was given to 14 patients with advanced breast cancer. Thereafter a regular daily dose of 30 mg of tamoxifen was given. Serum and urine levels of tamoxifen and metabolites were measured by high-performance liquid chromatography and compared with levels determined in 31 patients with advanced breast cancer at the steady state at a daily dose of 30 mg of tamoxifen. Results: Serum and urine levels (24-h values) of tamoxifen and metabolites were lower (P<0.05) after a loading dose than at the steady state. The difference was most pronounced for the metabolites, whereas the tamoxifen loading-dose level was near the steady state. Conclusion: Tamoxifen steady state can be reached in 1–2 days by the administration of a loading dose of 160 mg of tamoxifen for 2 days. Tamoxifen metabolite steady-state levels are reached regularly after 4 or more weeks during application of a loading dose. Very little tamoxifen or metabolites are excreted into the urine.
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Received: 17 December 1997 / Accepted: 2 June 1998
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de Vos, D., Slee, P., Briggs, R. et al. Serum and urine levels of tamoxifen and its metabolites in patients with advanced breast cancer after a loading dose and at steady-state levels. Cancer Chemother Pharmacol 42, 512–514 (1998). https://doi.org/10.1007/s002800050854
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DOI: https://doi.org/10.1007/s002800050854