Tamoxifen is indicated for the treatment of metastatic breast cancer in women and men and ductal carcinoma in Situ.
Tamoxifen belongs to a class of drugs called selective estrogen receptor modulators (SERMs), which have both estrogenic and antiestrogenic effects. Tamoxifen has the same nucleus as diethylstilbestrol but possesses an additional side chain (trans isomer) which accounts for its antiestrogenic activity.
Mode of Action:
Tamoxifen is a nonsteroidal agent that binds to estrogen receptors (ER), inducing a conformational change in the receptor. This results in a blockage or change in the expression of estrogen dependent genes. The prolonged binding of tamoxifen to the nuclear chromatin of these results in reduced DNA polymerase activity, impaired thymidine utilization, blockade of estradiol uptake, and decreased estrogen response. It is likely that tamoxifen interacts with other coactivators or corepressors in the tissue and binds with different estrogen receptors, ER-alpha or ER-beta, producing both estrogenic and antiestrogenic effects.
Signs observed at the highest doses following studies to determine LD50 in animals were respiratory difficulties and convulsions.
Jordan VC: Tamoxifen (ICI46,474) as a targeted therapy to treat and prevent breast cancer. Br J Pharmacol. 2006 Jan;147 Suppl 1:S269-76. PubmedJordan VC: Fourteenth Gaddum Memorial Lecture. A current view of tamoxifen for the treatment and prevention of breast cancer. Br J Pharmacol. 1993 Oct;110(2):507-17. PubmedHowell A, Cuzick J, Baum M, Buzdar A, Dowsett M, Forbes JF, Hoctin-Boes G, Houghton J, Locker GY, Tobias JS: Results of the ATAC (Arimidex, Tamoxifen, Alone or in Combination) trial after completion of 5 years’ adjuvant treatment for breast cancer. Lancet. 2005 Jan 1-7;365(9453):60-2. PubmedSteiner AZ, Terplan M, Paulson RJ: Comparison of tamoxifen and clomiphene citrate for ovulation induction: a meta-analysis. Hum Reprod. 2005 Jun;20(6):1511-5. Epub 2005 Apr 21. Pubmedvan Bommel EF, Hendriksz TR, Huiskes AW, Zeegers AG: Brief communication: tamoxifen therapy for nonmalignant retroperitoneal fibrosis. Ann Intern Med. 2006 Jan 17;144(2):101-6. PubmedFDA label
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