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Tamoxifen is a well-known drug discovered by what is now AstraZeneca. It was originally screened in a development program centered on the introduction of new contraceptive agents. Although it proved effective in rats, it was not a useful drug for control of fertility in women; it actually induced ovulation.
While commonly referred to as an anti-estrogen, this is not entirely accurate. In actual fact, tamoxifen is more appropriately described as a selective estrogen receptor modulator. This is because it expresses both estrogenic and antiestrogenic actions, depending on the target tissue.
On mammary epithelium, its actions are strongly antiestrogenic, which is why it’s used in both the prevention and treatment of breast cancer. In contrast, on uterine epithelium its action is proestrogenic, which has fuelled the current controversy regarding its safety in cancer prevention. This is especially since an increased incidence of endometrial carcinoma has been found in women treated chronically with tamoxifen.
Tamoxifen comes as a pill to be taken once or twice daily with water and each day at a similar time. When taken, the tablets should be whole; they should not be split, chewed, or crushed. Should a person forget to take a dose of tamoxifen, they should take the missed dose as soon as they remember it, and take the next dose as is usual. However, if it is almost time for their next dose, they should ignore the missed dose and continue following the regular dosing schedule. A double dose should never be taken to compensate for a missed one.
Tamoxifen therapy is used in a number of cases:
For example; Women who have had treatment for DCIS (intraductal carcinoma - a less common type of breast cancer ) through surgery, chemotherapy and/or radiation are at high risk for developing invasive breast cancer in the future, and hormone therapy (with tamoxifen) prevents the development of this cancer in a great deal of women within the first five years of treatment.
The safety of tamoxifen therapy has not been established in children or in those breastfeeding due to the potential for carcinogenicity. However, the benefits of Tamoxifen therapy generally outweigh the risks in those who are able to have the therapy. With regards to these risks, the associated adverse reactions tend to be minor, well-tolerated and often easily controlled by dose reduction. The side effects include: