Action

Competes with estrogen receptors in tumor cells for binding to target tissues (such as breast); reduces DNA synthesis and estrogen response

Availability

Oral solution: 10 mg/5 ml

Tablets: 10 mg, 20 mg

Tablets (enteric-coated): 20 mg

Indications and dosages

➣ Adjunctive treatment of breast cancer

Adults: 20 to 40 mg P.O. daily for 5 years. Daily dosages of 20 mg may be taken as a single dose; daily dosages above 20 mg should be divided and taken b.i.d. (morning and evening).

➣ To reduce breast cancer incidence in high-risk women; treatment of ductal carcinoma in situ

Adults: 20 mg P.O. daily for 5 years

Off-label uses

• Mastalgia

• Ovulation stimulation

Contraindications

• Hypersensitivity to drug

• Concurrent warfarin use

• Women with a history of deep-vein thrombosis or pulmonary embolism

• Pregnancy or breastfeeding

Precautions

Use cautiously in:

• decreased bone marrow reserve, leukopenia, thrombocytopenia, cataracts, hyperlipidemia

• females of childbearing age.

Administration

• Don't break or crush enteric-coated tablets.

• Know that drug is indicated for reducing breast cancer risk only in high-risk women, defined as those older than age 35 who have at least a 1.67% chance of developing breast cancer over 5 years.

Adverse reactions

CNS: confusion, depression, headache, weakness, fatigue, light-headedness

CV: chest pain, deep-vein thrombosis

EENT: blurred vision, ocular lesion, retinopathy, corneal opacity

GI: nausea, vomiting, abdominal cramps, anorexia

GU: vaginal bleeding, discharge, or dryness; irregular menses; amenorrhea; oligomenorrhea; ovarian cyst; pruritus vulvae; endometrial or uterine cancer

Hematologic: leukopenia, thrombocytopenia

Metabolic: hypercalcemia, fluid retention

Musculoskeletal: bone pain

Respiratory: cough, pulmonary embolism

Skin: skin changes, hair thinning or partial hair loss

Other: altered taste, weight loss, tumor flare, tumor pain, hot flashes, edema

Interactions

Drug-drug. Aminoglutethimide, estrogens: decreased tamoxifen effects

Antineoplastics: increased risk of thromboembolic events

Bromocriptine: increased tamoxifen blood level

Warfarin: increased anticoagulant effect

Drug-diagnostic tests. Aspartate aminotransferase, bilirubin, calcium, creatinine, hepatic enzymes: increased levels

Platelets, white blood cells: decreased counts

Patient monitoring

• Monitor lipid panel, calcium level, mammography results, and gynecologic exam results.

Watch for signs and symptoms of thromboembolic events, including cerebrovascular accident and pulmonary embolism.

• Monitor menstrual cycle pattern for changes that may signal endometrial or uterine cancer.

Patient teaching

• Tell patient to swallow enteric-coated tablets whole without breaking or crushing.

Instruct patient to immediately report leg or calf pain, swelling, or tenderness; unexpected shortness of breath; sudden chest pain; coughing up blood; new breast lumps; vaginal bleeding; menstrual irregularities; changes in vaginal discharge; pelvic pain or pressure; and vision changes.

• Inform patient that increase in bone or tumor pain usually means drug will be effective. Advise her to discuss pain management with prescriber.

• Stress importance of undergoing regular blood tests, mammograms, and gynecologic exams to identify early signs of serious adverse reactions.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.