Aromatase Inhibitors

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Aromatase inhibitors

Definition

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

Purpose

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.

Description

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

Precautions

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.

Anastrazole

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)

Exemestane

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

Letrozole

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

Interactions

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.