Tamoxifen citrate is a nonsteroidal agent that has demonstrated potent antiestrogenic effects related to its ability to compete with estrogen for binding sites in target tissues. Tamoxifen is an oral anti-estrogen and estrogen antagonist which competes with estrogen at the receptor sites reducing estrogenic expression. Tamoxifen citrate is a Selective Estrogen Receptor Modular (SERM) acting via estrogen site competition as opposed to Aromatase Inhibitor (AI) drugs such as Anastrol which prevent aromatase derived estrogens from being created.
The antiestrogenic effects of tamoxifen may be related to its ability to compete with estrogen for binding sites in target tissues such as breast. Tamoxifen inhibits the induction of rat mammary carcinoma induced by dimethylbenzanthracene (DMBA) and causes the regression of already established DMBA-induced tumors. In this rat model, tamoxifen appearsto exert its antitumor effects by binding the estrogen receptors. In cytosols derived from human breast adenocarcinomas, tamoxifen competes with estradiol for estrogen receptor protein.
Following a single oral dose of 20 mg tamoxifen, an average peak plasma concentration occurred approximately 5 hours after dosing. The decline in plasma concentrations of tamoxifen is biphasic with a terminal elimination half-life of about
5 to 7 days. After initiation of therapy, steady state concentrations for tamoxifen are achieved in about 4 weeks and steady-state concentrations for N-desmethyl tamoxifen are achieved in about 8 weeks, suggesting a half-life of approximately 14 days for this metabolite.
Tamoxifen is extensively metabolized after oral administration. N-desmethyl tamoxifen is the major metabolite. Other minor metabolites have been identified. Studies in women receiving 20 mg of 14C radio-labeled tamoxifen have shown that approximately 65% of the administered dose was excreted from the body over a period of 2 weeks.
INDICATION AND USAGE
Oncology: For adjuvant treatment of breast cancer, treatment of axillary node-negative breast cancer, treatment of ductal carcinoma in situ, and reduction of breast cancer in high risk women. Tamoxifen is frequently used as an antiestrogen in the treatment of metastatic mammary carcinoma, especially in post-menopausal women, and patients with endometrial cancer, renal cancer, soft tissues sarcoma, and pituitary tumors.
Fertility: For treatment of infertility in women with anovulatory disorders and oligospermia in men.
Male Elevated Estrogen: For use as an antiestrogen to reduce undesirable estrogen-linked expression in males with elevated estrogen levels either naturally or due to androgen therapy.
Testosterone Suppressed Males: For use in males with suppressed endogenous testosterone production due to androgen therapy after exogenous androgens have cleared.
Patients with known hypersensitivity to the drug or any of its ingredients.
Patients who require concomitant anticoagulant therapy.
Patients with a history of deep vein thrombosis, stroke, uterine malignancies, or pulmonary embolus.
Patients with history of ocular disturbances, cataracts, or retinopathy.
Patients with hypercalcaemia.
To be used only under the care of a physician.
For women: Tamoxifen may increase fertility.
Tamoxifen may cause fetal harm.
Tamoxifen has been linked to severe liver and thromboembolic events.
Monitor patients CBC and liver function tests.
Tamox 20 when used in combination with coumarin-type anticoagulants may create an anticoagulant effect. Careful monitoring of the patient's prothrombin time is recommended.
Concomitant administration of letrozole, anastrazole, phenobarbital, aminoglutethimide, or corticosteroids may result in decreased tamoxifen serum levels. Bromocriptine has been shown to elevate tamoxifen concentration in serum.
Most side effect studies are based on female cancer patients whose primary sex hormone estrogen is effectively blocked through the use of tamoxifen. Male patients have demonstrated reduced levels of side effects.
Side effects may include nausea, coughing, vomiting and hot flashes, difficulty breathing; swelling of your face, lips, tongue, or throat. Sudden numbness or weakness, especially on one side of the body, sudden headache, confusion, problems with vision, speech, or balance; chest pain, shortness of breath.
Reduced cognition and memory impairment, vaginal bleeding, amenorrhea, altered menses, discharge, ovarian cysts or pelvic pain. Corneal changes, reduced color vision, cataract formation, retinal dvt, and retinopathy.
Thromoembolic events, anorexia, pain, depression. Rarely elevation of liver enzymes and liver disease. Reduced platelet production, leukopenia, thrombocytopenia. hypercalcaemia, peripheral oedema, distaste for food, pruritis vulvae, depression, dizziness, light-headedness, headache, hair thinning, hair loss, and vaginal dryness.
Increases in serum triglycerides.Stop using tamoxifen and call your doctor at once if you experience any of these serious side effects.
DOSAGE AND ADMINISTRATION
Adult male estrogen management: 10 - 20mg taken orally every other day.
Adult male gynecomastia onset: 40mg taken orally for 3 days. Reduce dosing thereafter.
Endogenous testosterone restart post-androgen therapy: 20mg per day taken orally for 10 to 14 days.
Adult male fertility: pursuant to advice of qualified physician.
Adult carcinoma: pursuant to advice of qualified physician.
20mg uncoated tablets: 50 tablets in blisters.
Protect from light. Store at 15 - 25oC.
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