Aromatase Inhibitors

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Aromatase inhibitors


Aromatase inhibitors are a class of hormone drugs. They inhibit aromatase, an enzyme that regulates the production of estrogen.


The aromatase inhibitors decrease blood and tumor levels of estrogen in postmenopausal women. They are used to treat advanced forms of breast cancer in post-menopausal women whose disease has progressed following therapy with other antiestrogen therapy.


Aromatase inhibitors lower a postmenopausal woman's estrogen levels, thereby preventing the cancer cells that are dependent on estrogen from growing.

Anastrazole (trade name Arimidex)

Anastrazole is a non-steroidal aromatase inhibitor that lowers blood levels of estradiol to prevent the rapidly growing cancerous cells. It is usually used in post-menopausal women as a treatment for advanced breast cancer that has not responded to other therapies, or it can be used as first-line therapy in these patients.

Exemestane (trade name Aromasin)

Exemestane is an aromatase inhibitor that reduces the concentration of estradiol in the bloodstream. It is also called an aromatase inactivator because it inactivates aromatase irreversibly, potentially providing continued benefits after treatment is stopped. It is used to treat advanced breast cancers in postmenopausal women whose cancers have not responded to other antiestrogen therapies.

Letrozole (trade name Femara)

Letrozole is a non-steroidal aromatase inhibitor that lowers blood estrogen levels by hindering the conversion of androgens to estrogens. It is used in postmenopausal women with advanced breast cancer that has progressed while on other antiestrogen therapy.

Recommended dosage

  • Anastrazole: The adult dose is 1 mg a day by mouth
  • Exemestane: The adult dose is 25 mg a day by mouth, after a meal
  • Letrozole: The adult dose is 2.5 mg a day by mouth


Aromatase inhibitors are not used in pregnant women because of the risk to the fetus. Since these drugs are generally prescribed for postmenopausal women, pregnancy is not usually an issue.

Except in life-threatening conditions, anastrazole, exemestane, and letrozole are not used in pregnancy because of risks to the fetus. These drugs should be avoided by those allergic to it and by nursing mothers.

Side effects

The aromatase inhibitors are generally tolerated quite well. Side effects are similar to the effects of decreased estrogen, such as hot flashes. The specific side effects are discussed in this section. People should report any side effects to the doctor.


Rash is the most common side effect of anastrazole. Less common side effects include:

  • hot flashes
  • headache, light-headedness, dizziness, confusion
  • depression, insomnia, anxiety
  • chest pain, high blood pressure, obstruction of blood vessels
  • nausea and vomiting , diarrhea , constipation, abdominal pain
  • dry mouth, altered taste, appetite loss
  • vaginal bleeding, vulvar itching
  • hair thinning
  • bone pain, tumor pain, weakness, muscle aches
  • cough, sinusitis
  • abnormally low red blood cell levels (anemia )
  • abnormally low white blood counts (leukopenia)


Side effects include:

  • hot flashes
  • headache, fatigue , insomnia
  • depression, anxiety
  • high blood pressure
  • nausea, vomiting
  • increase in appetite
  • diarrhea, constipation, abdominal pain
  • cough, difficulty breathing


Common side effects include:

  • headache
  • nausea, vomiting
  • lethargy
  • appetite loss (anorexia )
  • rash, itching

Less common side effects include:

  • drowsiness, dizziness
  • depression, anxiety
  • high blood pressure
  • constipation, diarrhea, heartburn
  • hair loss
  • hot flashes, sweating
  • cough, difficulty breathing


Patients who are taking any kind of prescription drug, over-the-counter drug, or herbal remedy should notify their physician before beginning any treatment with aromatase inhibitors.

See Also Megestrol acetate; Tamoxifen

Rhonda Cloos, R.N.



A steroid that has some of the properties of estrogen.