Breast Cancer Uses, Warnings, Side Effects, Dosage

What is anastrozole, and what is it used for?

Anastrozole is a medication used in the treatment of certain types of breast cancer in postmenopausal women. Anastrozole is used in different stages of breast cancer to prevent, halt or slow down the progression of cancer growth.

Anastrozole belongs to a drug class known as aromatase inhibitors which work by blocking the activity of aromatase, an enzyme that plays an important role in the biosynthesis of estrogens, the female sex hormones. 

Estrogens are steroid hormones that come in three forms, estrone (E1), estradiol (E2) and estriol (E3). Estrogens are essential for normal sexual development and function, and in addition, have many other important functions in the body. On the downside, the growth of majority of breast cancers is stimulated and maintained by estrogens.

In postmenopausal women, the ovaries stop producing estrogens and the primary source of estrogens are those derived from the male sex hormones (androgens) androstenedione and testosterone produced by the adrenal gland. Aromatase is responsible for the conversion of the two androgens into estrone and estradiol. By inhibiting aromatase, anastrozole reduces the availability of estrogens that the cancer cells require to grow.

Anastrozole is a selective non-steroidal aromatase inhibitor and does not affect corticosteroids or aldosterone, the other hormones produced by the adrenal gland. Anastrozole is beneficial only in the treatment of estrogen-responsive breast cancers in postmenopausal women and has no benefits for premenopausal women.

Anastrozole is approved by the FDA for the following breast cancer treatments:

• Adjuvant therapy after primary treatment of postmenopausal women with hormone receptor-positive early breast cancer, to lower the risk of its return.
• First-line treatment of postmenopausal women with hormone receptor-positive or hormone receptor unknown locally advanced or metastatic breast cancer.
• Second-line treatment of advanced breast cancer in postmenopausal women with disease progression following tamoxifen therapy. Point to note, patients with estrogen receptor-negative disease and patients who did not respond to previous tamoxifen therapy rarely responded to anastrozole.

What are the side effects of anastrozole?

Common side effects of anastrozole include:

Less common side effects of anastrozole include:

Call your doctor immediately if you experience any of the following symptoms or serious side effects while using this drug:

• Serious heart symptoms include fast or pounding heartbeats, fluttering in your chest, shortness of breath, and sudden dizziness;
• Severe headache, confusion, slurred speech, severe weakness, vomiting, loss of coordination, feeling unsteady;
• Severe nervous system reaction with very stiff muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, and feeling like you might pass out; or
• Serious eye symptoms include blurred vision, tunnel vision, eye pain or swelling, or seeing halos around lights.

This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.

What are the dosages of anastrozole?

Tablet

Adult:

Breast Cancer

Adjuvant treatment

• 1 mg orally every day for 5 years

First-line treatment

• 1 mg orally every day; continue until tumor progression

Second-line treatment

• 1 mg orally every day; continue until tumor progression

Dosage Modifications

Hepatic impairment

• Mild-to-moderate impairment or stable hepatic cirrhosis: Dose adjustment not necessary
• Severe hepatic impairment: Not studied

Administration

• May take with or without food

Pediatric:

Overdose

There is insufficient information on anastrozole overdose. There is no antidote for anastrozole, treatment includes symptomatic and supportive care along with close monitoring of the patient.

What drugs interact with anastrozole?

Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.

• Anastrozole has no known severe Interactions with other drugs.
• Serious Interactions of anastrozole include:
• Moderate Interactions of anastrozole include:
  • atogepant
  • avapritinib
  • axitinib
  • cholera vaccine
  • conjugated estrogens, vaginal
  • dengue vaccine
  • finerenone
  • flibanserin
  • isavuconazonium sulfate
  • ivacaftor
  • lemborexant
  • lomitapide
  • midazolam intranasal
  • siponimod
  • tazemetostat
  • tinidazole
• Mild Interactions of anastrozole include:
  • ruxolitinib
  • ruxolitinib topical

The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.

It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.

Pregnancy and breastfeeding

• Do not prescribe anastrozole to women who are pregnant or who may become pregnant. May cause fetal harm and is of no benefit to premenopausal women with breast cancer.
• There are no adequate and well-controlled studies on anastrozole treatment in pregnant women. In animal reproductive studies, anastrozole caused pregnancy failure, pregnancy loss and signs of delayed fetal development.
• Anastrozole treatment may impair fertility in women of reproductive potential.
• It is not known if anastrozole is present in breast milk. Many drugs are excreted in breast milk. Taking into account the maternal need for treatment, discontinue anastrozole or nursing because of the potential for serious adverse effects in the breastfed infant.

What else should I know about anastrozole?

• Take anastrozole exactly as prescribed.
• Stop taking anastrozole and contact your doctor if you:
  • Develop severe allergic symptoms
  • Have chest pain or shortness of breath
  • Become pregnant
• Anastrozole may not work if taken with other hormonal medications such as birth control.
• Store safely out of reach of children.
• In case of overdose, seek medical help or contact Poison Control.