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Anastrozole (Brand name Arimidex) is a drug of the class of aromatase inhibitors used to treat breast cancer in women who have gone through the menopause. Anastrozole works by cutting down the amount of the hormone called estrogen that your body makes. It does this by blocking a natural substance (an enzyme) in your body called ‘aromatase’.






Many breast cancers have estrogen receptors and growth of these tumors can be stimulated by estrogens. In post-menopausal women, the principal source of circulating estrogen (primarily estradiol) is conversion of adrenally-generated androstenedione to estrone by aromatase in peripheral tissues, such as adipose tissue, with further conversion of estrone to estradiol.

Anastrozole is a potent and selective non-steroidal aromatase inhibitor. It significantly lowers serum estradiol concentrations. As less estrogen reaches the cancer cells, they grow more slowly or stop growing altogether. Other aromatase inhibitors include letrozole (Femara®) and exemestane (Aromasin®).


  • Early breast cancer: Adjuvant treatment (After surgery) of postmenopausal women with hormone receptor-positive early breast cancer (cancer that has not spread), to reduce the chance of the cancer coming back.
  • Advanced breast cancer: First line treatment of postmenopausal women with hormone receptor-positive or hormone receptor unknown locally advanced or metastatic breast cancer.

Anastrozole offers no clinical benefit to premenopausal women with breast cancer. The main source of estrogen is the ovaries in premenopausal women, while in post-menopausal women most of the body's estrogen is produced in peripheral tissues. In premenopausal women, aromatase inhibitors have a limited ability to reduce circulating estrogen. Unlike postmenopausal women, premenopausal women have a large amount of aromatase substrate present in the ovary. When aromatase inhibitors are used in premenopausal women, the decrease in estrogen activates the hypothalamus and pituitary axis to increase gonadotropin secretion, which in turn stimulates the ovary to increase androgen production. Thus, aromatase inhibitors are generally not given to premenopausal women for breast cancer treatment without the addition of a medication to suppress the rise in gonadotrophins and subsequent increase in hormone levels.


  • Anastrozole may be used in children with precocious puberty, or children with pubertal gynecomastia.
  • Some athletes and body builders use anastrozole as part of their steroid cycle to reduce and prevent symptoms of excess estrogen; in particular, gynecomastia and water retention.

[edit] DOSAGE

One 1 mg tablet once a day. It should be swallowed whole with a glass of water, at about the same time each day. It doesn't matter whether this is in the morning or evening

For postmenopausal women with hormone receptor-positive early invasive breast cancer, the recommended duration of adjuvant Anastrozole treatment is 5 years.

Patients with hormone receptor positive early breast cancer who switched to Anastrozole after 2 years of adjuvant treatment with tamoxifen had a significant improvement in disease free survival compared to patients who remained on tamoxifen.[1]


  • Pregnancy and breastfeeding.
  • Patients with known hypersensitivity to Anastrozole


  • In women with pre-existing ischemic heart disease, an increased incidence of ischemic cardiovascular events was observed with Anastrozole. Consider risk and benefits of therapy in patients with pre-existing ischemic heart disease.
  • Decrease in bone mineral density: Anastrozole lowers circulating estrogen levels, so it may cause a reduction in bone mineral density with a possible consequent increased risk of fracture. Consider bone mineral density monitoring.
  • Increases in total cholesterol may occur. Consider cholesterol monitoring.


  • Tamoxifen: Do not use in combination with Anastrozole. No additional benefit seen over tamoxifen monotherapy.
  • Estrogen-containing products: Combination use may diminish activity of Anastrozole


  • Pregnancy Category X (US). Anastrozole is contraindicated in women who are or may become pregnant. In animal studies, anastrozole caused pregnancy failure, increased pregnancy loss, and signs of delayed fetal development. If Anastrozole is used during pregnancy, or if the patient becomes pregnant while receiving this drug, the patient should be apprised of the potential hazard to the fetus and potential risk for pregnancy loss.
  • Nursing Mothers: It is not known if anastrozole is excreted in human milk. A decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.


Anastrozole is generally well tolerated, possible adverse effects include:

  • Hot flushes and sweats (usually mild and may wear off after a period of time)
  • Asthenia, fatigue and Somnolence especially at the start of treatment
  • Nausea and vomiting (usually mild). these side effects can be relieved by taking your tablet with food or at night.
  • Headache (Not common)
  • Musculoskeletal disorders (Joint pains and muscular stiffness)
  • Vaginal bleeding (Rarelly and usually in the first few weeks of treatment after changing from existing hormonal therapy to treatment with Anastrozole).
  • Vaginal dryness (Vaginal moisturisers or lubricants can be helpful)
  • Diarrhea
  • Hair thinning (alopecia). this side effect is usually mild and the hair grows back at the end of treatment.
  • Skin rashes
  • Risk of osteoporosis. Anastrozole increases the risk of fracture compared with tamoxifen.
  • Hypercholesterolemia

Anastrozole is not associated with the estrogen-like adverse effects of tamoxifen (Tamoxifen blocks the effects of estrogen in breast tissue BUT ACTS LIKE ESTROGEN in the uterus and bone: Tamoxifen has been associated with endometrial hyperplasia, fibroids, polyps, and endometrial tumors and may increase bone density)


Adjuvant Hormonal Therapy for Breast Cancer