Tamoxifen Citrate

A to Z Drug Facts

 Action A nonsteroidal agent with antiestrogenic properties. The half-life is about 14 days. Fecal excretion is the primary route of elimination.

 Indications Breast carcinoma in women, metastatic breast carcinoma in men and women, reduction in risk of breast cancer in high-risk women, lower risk of invasive breast cancer in women with ductal carcinoma in situ (DCIS). Unlabeled use(s): Mastalgia; decreasing the size and pain of gynecomastia.

 Contraindications Hypersensitivity to drug; women who require concomitant coumarin-type anticoagulant therapy; women with a history of deep vein thrombosis or pulmonary embolus (reduction in breast cancer incidence and DCIS indications).

 Route/Dosage

Tamoxifen Alone as Adjunct to Surgery

ADULTS: PO 20 mg/day in 1 to 2 divided doses. Duration of therapy of more than 2 yr is most effective.

Combination Chemotherapy as Adjunct to Surgery

ADULTS: PO 10 mg bid in postmenopausal women or women over 50 yr with positive axillary nodes for 5 yr.

Advanced Breast Carcinoma in Postmenopausal Women

ADULTS: PO 10 to 20 mg bid. Response to therapy should occur within 4 to 10 wk.

Prevention of Breast Cancer in High-Risk Women

ADULTS: PO 20 mg/day in 1 to 2 divided doses. Continue for 5 yr.

 Interactions

Aminoglutethimide, phenobarbital: Tamoxifen concentrations may be reduced.

Bromocriptine: Tamoxifen concentrations may be increased.

Tacrolimus, other drugs metabolized by cytochrome P450 3A4 (eg, amitriptyline, carbamazepine, cyclosporine, lovastatin, sertraline, verapamil): Coadministration may result in reduced clearance and increased serum concentrations of these agents.

Warfarin: Increased hypoprothrombinemic effect.

 Lab Test Interferences T₄ elevations; increased AST; increased bilirubin; increased creatinine. Variations in the karyopyknotic index on vaginal smears and various degrees of estrogen effect on Pap smears. In oligospermic males treated with tamoxifen, LH, FSH, testosterone, and estrogen levels were elevated.

 Adverse Reactions

CV: Peripheral edema. CNS: Headache; dizziness; depression. DERM: Rash. ENDO: Hot flashes. GI: Moderate to low potential for nausea and vomiting; food distaste. GU: Vaginal discharge, pruritus vulvae. META: Hypercalcemia. MUSC: Bone and tumor pain at initiation of therapy; soft tissue lesions can increase in size. SPEC: Retinopathy; superficial corneal opacity. OTHER: At doses of 40 mg/day, tamoxifen has an increased risk of endometrial cancer.

 Precautions

Pregnancy: Category D. Lactation: Undetermined. Cardiovascular: Life-threatening events, including stroke and pulmonary embolism, may occur. Children: Safety and efficacy in pediatric patients not established. Disease of bone: Increased bone pain, tumor pain, and local disease flare are sometimes associated with a good tumor response shortly after starting tamoxifen, and generally subside rapidly. Hepatic effects: Changes in liver enzyme levels. Hypercalcemia: If hypercalcemia occurs, institute appropriate measures and, if severe, discontinue use. Thromboembolic effects: Thromboembolic effects including deep vein thrombosis and pulmonary embolism. Uterine effects: Endometrial changes including hyperplasia, polyps, and uterine malignancies may occur. Visual disturbances: Visual disturbances, including corneal changes, cataracts, the need for cataract surgery, decrement in color vision perception, retinal vein thrombosis, and retinopathy have occurred with use.

 Administration/Storage

• Store at room temperature. Protect from light.
• Administer PO.

 Assessment/Interventions

• Monitor CBC periodically.
• Monitor periodic serum calcium levels during initial therapy in women with metastatic disease.
• Tamoxifen-related tumor flare may be managed with supportive care, temporarily stopping tamoxifen with reintroduction at 5 to 10 mg daily, and concomitant prednisone for 1 to 2 wk.
• Perform LFTs periodically.
• Perform breast examination, mammogram, and gynecologic examination prior to initiation of therapy for women taking tamoxifen to reduce the incidence of breast cancer.
• Repeat CBC, LFTs, and gynecologic examinations at regular intervals while on therapy.
• Periodic monitoring of plasma triglycerides and cholesterol may be indicated in patients with preexisting hyperlipidemias.

 Patient/Family Education

• Tamoxifen can induce ovulation.
• Tamoxifen reduces the incidence of breast cancer but may not eliminate risk.
• Women should have regular gynecologic examinations and promptly inform their health care provider of menstrual irregularities, abnormal vaginal bleeding, change in vaginal discharge, or pelvic pain or pressure.
• Women should not become pregnant during therapy.
• Notify health care provider of pain/swelling/tenderness of legs or calves, unexplained shortness of breath, changes in vision, new breast lumps, vaginal bleeding, gynecologic symptoms (eg, menstrual irregularities, changes in vaginal discharge, pelvic pain or pressure), sudden chest pain, or coughing up blood.

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Copyright © 2003 Facts and Comparisons
David S. Tatro
A to Z Drug Facts