Serum and urine levels of tamoxifen and its metabolites in patients with advanced breast cancer after a loading dose and at steady-state levels.
OBJECTIVE
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.


CONCLUSIONS
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.
de Vos
D
D
Medical Department Pharmachemie BV, Haarlem, The Netherlands.
Slee
P H
PH
Briggs
R J
RJ
Stevenson
D
D
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018931:Antineoplastic Agents, Hormonal / Q000008:administration & dosage / Q000097:blood / Q000627:therapeutic use* / Q000652:urine; D001943:Breast Neoplasms / Q000097:blood / Q000188:drug therapy* / Q000652:urine; D004334:Drug Administration Schedule; D006801:Humans; D008875:Middle Aged; D013629:Tamoxifen / Q000008:administration & dosage / Q000097:blood / Q000627:therapeutic use* / Q000652:urine
D018931:Antineoplastic Agents, Hormonal; D013629:Tamoxifen