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The adverse effects of enclomiphene have not been extensively studied. [10] Enclomiphene is a selective estrogen receptor modulator (SERM), which is associated with an increased risk of thrombo-embolic events. [11] Enclomiphene, unlike testosterone replacement therapy, is not associated with infertility or decreased spermatogenesis. [11]
Tamoxifen, sold under the brand name Nolvadex among others, is a selective estrogen receptor modulator used to prevent breast cancer in women and men. [13] It is also being studied for other types of cancer. [13] It has been used for Albright syndrome. [14] Tamoxifen is typically taken daily by mouth for five years for breast cancer. [14]
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.
Toremifene appears to be safer than tamoxifen. [15] It has a lower risk of venous thromboembolism (VTE) (e.g., pulmonary embolism), stroke, and cataracts. [15] The lower risk of VTE may be related to the fact tamoxifen decreases levels of the antithrombin III to a significantly greater extent than either 60 or 200 mg/day toremifene. [15]
Clomifene is a prodrug being activated via similar metabolic pathways as the related triphenylethylene SERMs tamoxifen and toremifene. [36] [37] The affinity of clomifene for the ER relative to estradiol ranges from 0.1 to 12% in different studies, which is similar to the range for tamoxifen (0.06–16%).
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.
Clinical studies of raloxifene for metastatic breast cancer in women have been conducted but found little effectiveness at 60 mg/day in those previously treated with tamoxifen, though modest effectiveness has been observed at higher doses. [14] [51] In contrast to tamoxifen, raloxifene is not approved for the treatment of breast cancer. [52]
Tamoxifen is currently first-line treatment for nearly all pre-menopausal women with hormone receptor-positive breast cancer. [1] Raloxifene is another partial agonist SERM which does not seem to promote endometrial cancer , and is used primarily for chemoprevention of breast cancer in high-risk individuals, as well as to prevent osteoporosis ...