Tamona20 mg

Tamoxifen citrate is a selective oestrogen receptor modulator (SERM) used for:

• Treatment of metastatic breast cancer in women and men, particularly those whose tumours are oestrogen receptor-positive
• Adjuvant treatment of node-positive breast cancer in women following mastectomy or breast-conserving surgery, axillary dissection, and breast irradiation
• Reduction of breast cancer incidence in women at high risk, based on age, family history, and other risk factors
• Reduction of the risk of invasive breast cancer in women with ductal carcinoma in situ (DCIS), following surgery and radiation

Tamoxifen carries a boxed warning specific to its use in the risk-reduction setting (DCIS and high-risk women without cancer), given the serious risks it carries relative to the benefit in these specific populations; the benefit clearly outweighs the risk in women already diagnosed with breast cancer.

Contains Tamona 20 mg as the active ingredient, available as oral tablets, commonly in 10 mg and 20 mg strengths (equivalent to a range of tamoxifen base doses).

Tamoxifen is a selective oestrogen receptor modulator that has been a cornerstone of breast cancer treatment for decades, used both to treat oestrogen receptor-positive breast cancer and, in specific high-risk populations, to reduce the chance of developing breast cancer in the first place. It works by blocking oestrogen's effect on breast tissue, competing with oestrogen for its receptor. However, tamoxifen has a complex, tissue-specific action: while it blocks oestrogen's effect in breast tissue, it can act like oestrogen in the uterus, which is the basis for its boxed warning regarding an increased risk of uterine cancer (endometrial adenocarcinoma and uterine sarcoma), alongside an increased risk of stroke and pulmonary embolism, particularly relevant when tamoxifen is used for risk reduction rather than to treat existing cancer.

Therapeutic Class: Selective Estrogen Receptor Modulator (SERM) / Antineoplastic

Tamoxifen has demonstrated potent antiestrogenic activity in breast tissue, competing with oestrogen for binding to the oestrogen receptor. This same competitive binding, however, produces oestrogen-agonist (oestrogen-like) effects in other tissues, notably the uterus and, to some degree, bone, which underlies both some of its beneficial effects (such as maintaining bone density in postmenopausal women) and its most serious risk (uterine malignancy).

• Taken orally, with or without food
• Doses above 20 mg/day are given in divided doses (morning and evening)
• Take at approximately the same time(s) each day
• Attend all scheduled gynaecological check-ups and report any abnormal vaginal bleeding, discharge, or pelvic pain promptly, given the uterine cancer risk

The following interactions are particularly important:

• Warfarin and other anticoagulants: tamoxifen can significantly enhance the anticoagulant effect of warfarin, increasing bleeding risk; concurrent use of a warfarin-type anticoagulant is contraindicated in the risk-reduction setting (DCIS/high-risk women), and requires close INR monitoring if used together for breast cancer treatment.
• Strong CYP2D6 inhibitors (such as certain antidepressants, including paroxetine and fluoxetine): may reduce the formation of tamoxifen's active metabolite, potentially reducing its effectiveness; consider alternative antidepressants where feasible in patients on tamoxifen who need treatment for depression or hot flushes.
• Other hormonal therapies: concurrent use with hormone replacement therapy is generally avoided, given opposing or unpredictable effects.
• Chemotherapy: when tamoxifen is coadministered with chemotherapy, there is a further increase in the risk of thromboembolic events.

Common side effects

• Hot flushes
• Fluid retention
• Nausea
• Vaginal discharge or bleeding
• Skin rash
• Fatigue

Serious side effects (boxed warning and other important effects - require prompt medical attention)

• Uterine malignancies: an increased incidence of endometrial adenocarcinoma and uterine sarcoma (sometimes fatal) has been reported with tamoxifen use; report any abnormal vaginal bleeding, discharge, or pelvic pain promptly, and attend regular gynaecological check-ups.
• Stroke - an increased incidence has been observed, particularly in the risk-reduction setting; report sudden weakness, confusion, or difficulty speaking immediately.
• Pulmonary embolism and deep vein thrombosis: report sudden shortness of breath, chest pain, or leg swelling and pain immediately.
• Ovarian cysts, endometriosis, and uterine fibroids have been reported.
• Menstrual irregularity or amenorrhoea.
• Cataract formation and the need for cataract surgery, observed more frequently with tamoxifen use.
• Liver changes, including rare reports of severe liver events.

Pregnancy

Tamoxifen must not be given during pregnancy, given the risk of fetal harm based on its hormonal mechanism of action. Effective non-hormonal contraception is recommended during treatment for women of childbearing potential.

Breastfeeding

Tamoxifen is not recommended during breastfeeding; discuss alternatives with your doctor if breastfeeding is planned.

• Uterine cancer risk (boxed warning): patients should be counselled about symptoms of uterine malignancy (abnormal vaginal bleeding, pelvic pain, or pressure) and undergo regular gynaecological examination.
• Stroke and pulmonary embolism risk (boxed warning): particularly relevant in the risk-reduction setting; discuss individual risk factors with your doctor before starting.
• Careful risk-benefit discussion is essential before starting tamoxifen for risk reduction (in women without a cancer diagnosis), given these serious potential risks weighed against the benefit of reduced breast cancer incidence; the benefit clearly outweighs the risk in women already diagnosed with breast cancer.
• Monitor for signs of thromboembolic events throughout treatment, particularly in patients with additional risk factors.
• Regular eye examinations may be recommended, given the increased incidence of cataracts.

Overdose of tamoxifen may cause exaggerated known effects, including QT prolongation reported in some overdose cases; general symptoms may include nausea, vomiting, dizziness, and, in significant overdose, more serious systemic effects. Suspected significant overdose requires prompt medical evaluation; treatment is generally supportive, provided in a medical facility, with cardiac monitoring considered given reported QT effects.

Store at room temperature, protected from light and moisture, as directed on the product label.

• Premenopausal women with metastatic breast cancer: Tamoxifen is used as an alternative to oophorectomy or ovarian irradiation.
• Men with breast cancer: Tamoxifen citrate tablets are effective in the treatment of metastatic breast cancer in men as well as women.
• Hepatic impairment: Use with caution, given hepatic metabolism of tamoxifen; monitor liver function as clinically indicated.
• Girls with McCune-Albright syndrome and precocious puberty: Used in some specialist settings, with continued monitoring for long-term uterine effects recommended, given the increased incidence of endometrial changes seen in adults on tamoxifen; long-term effects in girls have not been established beyond 1 year of treatment in formal studies.

For adjuvant breast cancer treatment, tamoxifen is commonly continued for 5 years or longer, per current oncology guidelines and individual risk assessment. For metastatic breast cancer, treatment continues until disease progression. For breast cancer risk reduction and DCIS, a 5-year course is standard. Duration is always determined by the treating oncologist based on the specific clinical situation.

Drug Class: Nonsteroidal triphenylethylene derivative, selective oestrogen receptor modulator

Tamoxifen competes with oestrogen for binding to the oestrogen receptor in breast tissue, blocking oestrogen's growth-stimulating effect on oestrogen receptor-positive breast cancer cells and on the breast tissue of women at high risk. This antiestrogenic action in breast tissue is the basis for both its cancer treatment and cancer-prevention effects. Paradoxically, tamoxifen behaves as an oestrogen-like agonist in the uterine lining, stimulating endometrial tissue growth, which is why it carries a specific, well-documented risk of uterine cancer.

Tamoxifen is not recommended for general use in children; it has been used in a specialist setting for precocious puberty associated with McCune-Albright syndrome in girls aged 2-10 years, with ongoing monitoring for uterine effects recommended, though long-term effects beyond 1 year of treatment in this population have not been established.