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[11] [7] Peak levels of tamoxifen after a single 40 mg oral dose were 65 ng/mL and steady state levels at 20 mg/day were 310 ng/mL. [5] Levels of tamoxifen show clear dose dependency across a dosage range of 1 to 20 mg/day. [5] [93] Endoxifen levels are approximately 5 to 10 times higher than afimoxifene levels, with large interindividual ...
Tamoxifen is a pure antiestrogenic trans-isomer and has differential actions at estrogen target tissues throughout the body. Tamoxifen is selectively antiestrogenic in the breast but estrogen-like in bones and endometrial cancer. [24] Tamoxifen undergo phase I metabolism in the liver by microsomal cytochrome P450 (CYP) enzymes.
Estrogen deprivation therapy, also known as endocrine therapy, is a form of hormone therapy that is used in the treatment of breast cancer.Modalities include antiestrogens or estrogen blockers such as selective estrogen receptor modulators (SERMs) like tamoxifen, selective estrogen receptor degraders like fulvestrant, and aromatase inhibitors like anastrozole and ovariectomy.
The first SERM, tamoxifen, was originally developed as an anti-estrogen contraceptive. However, it was discovered it promoted ovulation in humans by acting as an agonist in ovaries. The drug was then successfully repurposed as a treatment for breast cancer where it was found to act as a full antagonist in breast tissue. [14]
Sivifene (A-007) was initially thought to be a SERM due to its structural similarity to tamoxifen but it was subsequently found not to bind to the estrogen receptor (ER). [8] Tesmilifene (DPPE; YMB-1002, BMS-217380-01) is also structurally related to tamoxifen but similarly does not bind to the ER and is not a SERM. [9] [10]
As such, it can cause side effects such as gynecomastia and fluid retention. [1] The co-administration of an antiestrogen such as an aromatase inhibitor like anastrozole or a selective estrogen receptor modulator like tamoxifen can reduce or prevent such estrogenic side effects. [1] Metandienone has no progestogenic activity. [1]
The side effects of toremifene are similar to those of tamoxifen. [5] The most common side effect is hot flashes. [5] Other side effects include sweating, nausea, vomiting, dizziness, vaginal discharge, and vaginal bleeding. [5] [7] In women with bone metastases, hypercalcemia may occur. [5] Toremifene has a small risk of thromboembolic events. [5]
N-Desmethyltamoxifen (developmental code name ICI-55,548) is a major metabolite of tamoxifen, a selective estrogen receptor modulator (SERM). [1] [2] N-Desmethyltamoxifen is further metabolized into endoxifen (4-hydroxy-N-desmethyltamoxifen), which is thought to be the major active form of tamoxifen in the body.