Arimidex is a brand-name prescription medication. It’s used to treat breast cancer in women who’ve gone through menopause.

Specifically, Arimidex is approved to treat the following types of breast cancer:

  • Early hormone receptor-positive (HR+) breast cancer. For this type of cancer, Arimidex is given to lower the risk of the breast cancer coming back or spreading after it’s already been treated with surgery. This type of treatment is called adjuvant treatment. (Early breast cancer hasn’t spread out of either your breast or the lymph nodes in your armpit. And HR+ cancer is stimulated to grow by hormones, including estrogen.)
  • Locally advanced or metastatic breast cancer that’s either HR+ or HR-unknown. Locally advanced or metastatic breast cancer typically can’t be treated with surgery. For these conditions, Arimidex is given as a first-line treatment. With first-line treatment, the drug is the first treatment used for the cancer. (Locally advanced breast cancer has spread to nearby areas or lymph nodes, while metastatic breast cancer has spread to other parts of your body. And while HR+ breast cancer is stimulated to grow by hormones, HR-unknown cancer may or may not be encouraged to grow by hormones.)
  • Locally advanced or metastatic breast cancer that’s come back or spread after treatment with the cancer drug tamoxifen. For this use, Arimidex can be given to treat HR+, HR-negative (HR–), or HR-unknown breast cancer. However, if your breast cancer is estrogen receptor-negative (ER–), or it didn’t improve with tamoxifen treatment in the past, it’s unlikely to improve with Arimidex. (ER– cancer doesn’t need estrogen in order to grow.)

Arimidex contains the drug anastrozole. It’s a hormone therapy used for breast cancer. Hormone therapies for breast cancer work by stopping estrogen from stimulating the cancer to grow. Specifically, Arimidex is a type of hormone therapy called an aromatase inhibitor. It works by lowering the amount of estrogen that your body makes.

Arimidex comes as a 1-mg tablet that’s taken by mouth once a day.

Effectiveness

One large clinical study showed that Arimidex was more effective than the cancer drug tamoxifen in treating early HR+ breast cancer.

The study compared women with early HR+ breast cancer who took tamoxifen for 5 years to women who took Arimidex for 5 years. Compared to those taking tamoxifen, women taking Arimidex had a 17% lower risk of:

  • their cancer coming back
  • their cancer spreading to other parts of their body
  • developing new cancer in their other (unaffected) breast
  • death caused by any reason

For advanced breast cancer, studies have shown that Arimidex treatment was either more effective or similarly effective to tamoxifen treatment.

For more information about the effectiveness of Arimidex, see the “Arimidex uses” section below.

Arimidex contains the active drug anastrozole.

Generic forms of Arimidex are available. A generic drug is an exact copy of the active drug in a brand-name medication. The generic is considered to be just as safe and effective as the original drug. Generics also tend to cost less than brand-name drugs.

Arimidex can cause mild or serious side effects. The following lists contain some of the key side effects that may occur while taking Arimidex. These lists do not include all possible side effects. And your side effects may vary from those listed below depending on the condition you’re using Arimidex to treat.

For more information on the possible side effects of Arimidex, talk with your doctor or pharmacist. They can give you tips on how to deal with any side effects that may be bothersome.

Note: The Food and Drug Administration (FDA) tracks side effects of drugs they have approved. If you would like to report to the FDA a side effect you’ve had with Arimidex, you can do so through MedWatch.

When side effects of Arimidex may start

It’s possible to have certain side effects of Arimidex very soon after you start taking the medication. This is because Arimidex lowers your body’s estrogen level by about 70% within 24 hours of when you start taking the drug. This action may lead to side effects that are similar to those seen with menopause, such as hot flashes or trouble sleeping.

Other side effects can take much longer to develop. This includes side effects such as thinning and weakening of your bones and increased cholesterol levels. You’re unlikely to notice side effects such as these, but your doctor will monitor you for them.

How long side effects of Arimidex may last

It’s hard to say how long your side effects will last, as each person’s reaction to the drug can be different. How long you’ll have side effects from the drug depends on how your body reacts to Arimidex.

If you’re concerned about side effects that don’t seem to be improving, talk with your doctor. They can recommend ways to help you manage the side effects.

Mild side effects

The mild side effects* of Arimidex can include:

  • hot flashes
  • feeling weak
  • fatigue (lack of energy)
  • pain, which may affect your joints, back, or bones
  • arthritis (inflammation in your joints)
  • nausea and vomiting
  • rash
  • insomnia (trouble sleeping)
  • headache
  • peripheral edema (swelling in your legs, ankles, or feet that’s caused by fluid retention)
  • lymphedema (buildup of lymphatic fluid in the tissues of your arm, which causes swelling in the area)
  • sore throat
  • dizziness
  • mood changes, such as depression
  • carpal tunnel syndrome (a nerve condition that affects your wrist), which may cause pain, tingling, or numbness in your hand

* This is a partial list of mild side effects of Arimidex. To learn about other mild side effects, talk with your doctor or pharmacist, or view the drug’s prescribing information.

Most of these side effects may go away within a few days or a couple of weeks. But if they become more severe or don’t go away, talk with your doctor or pharmacist.

Serious side effects

Serious side effects from Arimidex aren’t common, but they can occur. Call your doctor right away if you have serious side effects. Call 911 if your symptoms feel life threatening or if you think you’re having a medical emergency.

Serious side effects and their symptoms can include:

  • Liver problems, such as hepatitis (inflammation in your liver). Symptoms can include:
    • generally not feeling well
    • pain on the right side of your belly
    • jaundice (yellowing of your skin or the whites of your eyes)
  • Skin reactions. Symptoms can include:
    • skin sores or ulcers
    • blisters

Other serious side effects, explained in more detail below in “Side effect details,” include:

Side effect details

You may wonder how often certain side effects occur with this drug. Here’s some detail on several of the side effects this drug may cause.

For the side effects described below, results from clinical studies of women with either early breast cancer or advanced breast cancer are shown.

With early breast cancer, the cancer hasn’t spread out of either your breast or the lymph nodes in your armpit. But with advanced breast cancer, the cancer has either spread to nearby areas or lymph nodes (called locally advanced breast cancer) or spread to other parts of your body (called metastatic breast cancer).

Allergic reaction

As with most drugs, some people can have an allergic reaction after taking Arimidex. But it’s not known how often this occurs in people using Arimidex.

Symptoms of a mild allergic reaction can include:

  • skin rash
  • itchiness
  • flushing (warmth and redness in your skin)

A more severe allergic reaction is rare but possible. Symptoms of a severe allergic reaction can include:

  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your tongue, mouth, or throat
  • trouble breathing

Call your doctor right away if you have a severe allergic reaction to Arimidex. Call 911 if your symptoms feel life threatening or if you think you’re having a medical emergency.

Reduced bone mineral density

It’s possible to have reduced bone mineral density (weakened bones) with Arimidex treatment.

Estrogen helps to keep your bones strong. But Arimidex lowers your estrogen levels. This means the drug can weaken your bones and increase your risk of osteoporosis (thin, weak bones) or bone fractures. But keep in mind that the increased risk of breaking a bone goes away after you stop taking Arimidex.

In a clinical study of women with early breast cancer who took Arimidex for 5 years, 11% developed osteoporosis. And 10% of the women taking Arimidex had bone fractures. In comparison, of women who took the cancer drug tamoxifen for 5 years, 7% had osteoporosis. And 7% of the women had a bone fracture.

Your doctor may check your bone mineral density both before you start Arimidex and during your treatment. Checking your bone mineral density is how your doctor measures how strong your bones are. To do this, your doctor will order a type of X-ray test called a DEXA scan.

Depending on the result of your DEXA scan, your doctor may prescribe medication to help protect your bones. For example, they may recommend that you take a calcium and vitamin D supplement, a type of drug called a bisphosphonate, or both.

To help reduce the risk of weakened bones while you’re taking Arimidex, you can:

  • make sure you get enough calcium and vitamin D (either through your diet or by taking a supplement as recommended by your doctor)
  • routinely do weight-bearing exercises
  • avoid smoking
  • avoid drinking large amounts of alcohol

If you have questions about your risk of reduced bone mineral density while you’re taking Arimidex, talk with your doctor.

Raised cholesterol level

Arimidex may raise the level of fat (called cholesterol) in your blood. Having a high cholesterol level can increase your risk of having a heart attack or stroke. These risks are also increased if you have ischemic heart disease (a type of heart disease that’s caused by narrowed arteries in your heart).

In a clinical study of women with early breast cancer, increased cholesterol levels were seen in 9% of women who took Arimidex for 5 years. In comparison, 3.5% of women who took the cancer drug tamoxifen for 5 years had the same result.

However, in another study, raised cholesterol levels weren’t reported in women who took Arimidex for just 1 year.

Your doctor may order blood tests to monitor your cholesterol level while you’re taking Arimidex. If your cholesterol level rises too much, your doctor may recommend that you take a medication to lower the level.

You can reduce your risk of having an increased cholesterol level by:

  • not smoking
  • exercising regularly
  • eating a healthy diet

If you have questions about your risk of increased cholesterol with Arimidex treatment, talk with your doctor.

Side effects after 5 years of treatment

Both the mild and serious side effects of Arimidex that are listed above were seen in women who took the drug for up to 5 years.

Clinical studies of Arimidex followed women with early breast cancer who took the drug for 5 years. And the studies were continued for an additional 5 years after the women stopped taking the drug. No new side effects were reported during this additional time.

If you have concerns about the side effects that you may have after Arimidex treatment, talk with your doctor. They can discuss with you what you may expect after treatment.

Weight gain

Some people using Arimidex may gain weight during treatment. In fact, in a clinical study of women with early breast cancer, 9% of those taking Arimidex had weight gain. And 9% of women who took the cancer drug tamoxifen for 5 years had weight gain.

In studies of women with advanced breast cancer, 2% of those taking Arimidex had weight gain. In comparison, weight gain occurred in 2% of women taking tamoxifen and in 12% of women taking megestrol. (Megestrol is also a drug that’s used to treat breast cancer. But it can also increase people’s appetite.)

Both cancer itself and cancer treatments can often cause changes in your appetite and body weight. If you’re concerned about weight gain during breast cancer treatment, talk with your doctor. They can recommend ways to help you manage a weight that’s healthy for you.

Back or joint pain

You may have some pain in your back or joints while you’re taking Arimidex.

For example, in one clinical study of women with early breast cancer:

  • joint pain was reported in:
    • 15% of women who took Arimidex for 5 years
    • 11% of women who took the cancer drug tamoxifen for 5 years
  • back pain was reported in:
    • 10% of women who took Arimidex for 5 years
    • 10% of women who took tamoxifen for 5 years

Joint pain, achiness, and stiffness are common side effects of aromatase inhibitors, such as Arimidex. (Aromatase inhibitors are a class of medications.)

On average, joint pain seems to begin about 6 weeks after starting an aromatase inhibitor. And it may improve after the first year of taking the drug. Various studies have shown that these joint-related side effects can often be eased with gentle physical exercise, such as walking.

If you have pain in your joints or your back while you’re taking Arimidex, talk with your doctor. They can recommend ways to help manage your discomfort.

Fatigue

Taking Arimidex can make you feel either weak or fatigued (lacking energy).

In a clinical study of women with early breast cancer, weakness and fatigue occurred in 19% of women taking Arimidex for 5 years. And these side effects occurred in 18% of women taking the cancer drug tamoxifen for 5 years.

Fatigue and weakness are common side effects of cancer treatments. Because of this, it’s important to rest while you’re undergoing cancer treatment. However, the American Cancer Society also notes that staying active is important for managing fatigue. Talk with your doctor about what kind of physical activity is right for you. They can also recommend how much activity you should try to do.

If you feel weakness or fatigue during Arimidex treatment, talk with your doctor about the best ways to manage these side effects.

Heart palpitations (not a side effect)

Heart palpitations weren’t reported in clinical studies of Arimidex. (With heart palpitations, you may feel your heart flutter, race, or skip a beat.) However, other heart-related side effects, such as heart attack and angina, were rarely reported. (Angina is a type of chest pain that’s caused by the heart not getting enough oxygen.)

One long-term study found that women taking aromatase inhibitors had a higher risk of less serious heart-related side effects than did women taking tamoxifen. (Aromatase inhibitors are a class of medications that includes Arimidex.) These side effects included abnormal heartbeat patterns and problems with heart valves. However, more research is needed to confirm these findings.

If you have any heart problems, talk with your doctor about whether Arimidex is right for you.

If you have heart palpitations while you’re taking Arimidex, call your doctor right away. Also call your doctor if you have changes in your heartbeat pattern, new or worsening chest pain, or shortness of breath. But if your symptoms feel life threatening, call 911.

The following information describes Arimidex dosages that are commonly used or recommended. However, be sure to take the dosage your doctor prescribes for you. Your doctor will determine the best dosage to fit your needs.

Drug forms and strengths

Arimidex comes as 1-mg tablets that are taken by mouth.

Dosage for breast cancer

The usual dosage of Arimidex for breast cancer is one tablet taken once a day. It’s best to take your dose at the same time each day.

What if I miss a dose?

If you forget to take a dose of Arimidex, take the missed dose as soon as you remember. However, if it’s almost time for your next dose, just skip the missed dose and take your next dose as usual. Don’t take two doses together to make up for a missed dose.

To help make sure that you don’t miss a dose, try setting a reminder on your phone. A medication timer may be useful, too.

Will I need to use this drug long term?

Arimidex is meant to be used as a long-term treatment for breast cancer. If you and your doctor determine that Arimidex is safe and effective for you, you’ll likely take it long term.

The length of time that you’ll take this drug depends on the type of cancer you’re using it to treat. Below we describe the typical length of time that Arimidex is given. But to know for sure how long you should take Arimidex, talk with your doctor.

For advanced breast cancer

If you’re taking Arimidex to treat advanced breast cancer, you’ll usually take the drug for as long as your doctor feels this treatment is right for you. (With advanced breast cancer, the cancer has either spread to nearby areas or lymph nodes, called locally advanced breast cancer, or spread to other parts of your body, called metastatic breast cancer.)

For early breast cancer

If you’re taking Arimidex as adjuvant treatment of early breast cancer, you’ll usually take the drug for at least 5 years. Adjuvant treatment is used to lower the risk of your breast cancer coming back or spreading after it’s already been treated with surgery. (With early breast cancer, the cancer hasn’t spread out of either your breast or the lymph nodes in your armpit.)

It’s not currently known if Arimidex should be continued after these 5 years. And if so, it’s not known for how long after the first 5 years it should be taken.

Some studies found that breast cancer is less likely to come back if an aromatase inhibitor is taken for an additional 5 years after the first 5 years of adjuvant therapy. (Aromatase inhibitors are a class of medications.) With this approach to treatment, the drug would be taken for a total of 10 years. However, other studies didn’t show a benefit for extending the treatment beyond 5 the usual years.

In addition, one recent study found that taking Arimidex for a total of 10 years didn’t provide any more benefit than taking it for a total of 7 years.

How long you take Arimidex for early breast cancer will depend on how likely your breast cancer is to come back. It will also depend on your risk of side effects from treatment.

The Food and Drug Administration (FDA) approves prescription drugs such as Arimidex to treat certain conditions. Arimidex may also be used off-label for other conditions. Off-label use is when a drug that’s approved to treat one condition is used to treat a different condition.

Arimidex for breast cancer Arimidex is FDA-approved to treat breast cancer in women who’ve gone through menopause.

Specifically, Arimidex is used to treat the following types of breast cancer:

  • Early hormone receptor-positive (HR+) breast cancer. For this type of cancer, Arimidex is given to lower the risk of the breast cancer coming back or spreading after it’s already been treated with surgery. This type of treatment is called adjuvant treatment. (Early breast cancer hasn’t spread out of either your breast or the lymph nodes in your armpit. And HR+ cancer is stimulated to grow by hormones, including estrogen.)
  • Locally advanced or metastatic breast cancer that’s either HR+ or HR-unknown. Locally advanced or metastatic breast cancer typically can’t be treated with surgery. For these conditions, Arimidex is used as a first-line treatment. With first-line treatment, the drug is the first treatment used for the cancer. (Locally advanced breast cancer has spread to nearby areas or lymph nodes, while metastatic breast cancer has spread to other parts of your body. And while HR+ breast cancer is stimulated to grow by hormones, HR-unknown cancer may or may not be encouraged to grow by hormones.)
  • Locally advanced or metastatic breast cancer that’s come back or spread after treatment with the cancer drug tamoxifen. For this use, Arimidex can be given to treat HR+, HR-negative (HR–), or HR-unknown breast cancer. However, if your breast cancer is estrogen receptor-negative (ER–), or it didn’t improve with tamoxifen treatment in the past, it’s unlikely to improve with Arimidex. (ER– cancer doesn’t need estrogen in order to grow.)

Arimidex contains the drug anastrozole. It’s a hormone therapy used for breast cancer. Hormone therapies for breast cancer work by stopping estrogen from stimulating the cancer to grow. Specifically, Arimidex is a type of hormone therapy called an aromatase inhibitor. It works by lowering the amount of estrogen that your body makes.

Effectiveness for breast cancer

One large clinical study showed that Arimidex was more effective than tamoxifen in treating early HR+ breast cancer. (Tamoxifen is another hormone therapy used to treat cancer. It’s a standard treatment option for breast cancer, as recommended in current guidelines.)

The study compared women with early HR+ breast cancer who took tamoxifen for 5 years to women who took Arimidex for 5 years. Compared to those taking tamoxifen, women taking Arimidex had a 17% lower risk of:

  • their cancer coming back
  • their cancer spreading to other parts of their body
  • developing new cancer in their other (unaffected) breast
  • death

The women in this study were followed for an additional 5 years after they stopped taking Arimidex. After the additional 5 years, compared to women who took tamoxifen, the women who took Arimidex had a 14% lower risk of:

  • their cancer coming back
  • their cancer spreading to other parts of their body
  • developing new cancer in their other (unaffected) breast
  • death

For advanced breast cancer, studies have shown that Arimidex treatment was either more effective or similarly effective to tamoxifen treatment.

In one study of women with advanced breast cancer, first-line treatment with Arimidex was more effective than first-line treatment with tamoxifen in slowing down cancer growth and spread. In this study, 88% of the women had HR+ cancer. However, hormone receptor status wasn’t known for 11% of the women.

A second study of women with advanced breast cancer found Arimidex to be similarly effective as tamoxifen in slowing worsening of people’s cancer. In this study, 45% of women had HR+ cancer. But hormone receptor status wasn’t known for 54% of the women.

Two studies looked at women with advanced breast cancer that had come back or spread after treatment with tamoxifen. For these women, second-line treatment with Arimidex was similarly effective as treatment with another hormone therapy drug called megestrol.

Other uses for Arimidex

In addition to the uses listed above, Arimidex may be used off-label. Off-label drug use is when a drug that’s approved for one use is used for a different one that’s not approved. And you may wonder if Arimidex is used for certain other conditions. Below is information on other possible uses for X drug.

Arimidex for breast cancer treatment in premenopausal women (off-label use)

Arimidex isn’t FDA-approved to treat breast cancer in premenopausal women. (Women who haven’t gone through menopause are called premenopausal.) But sometimes the drug is used off-label in this group of women to treat hormone receptor-positive (HR+) cancers. With HR+ breast cancer, the cancer is encouraged to grow by hormones.

In fact, aromatase inhibitors (the class of drugs Arimidex belongs to) are listed as a breast cancer treatment option in current guidelines for premenopausal women.

It’s important to note that Arimidex works by stopping the aromatase enzyme (type of protein) from working in your body. This enzyme helps to make your body’s estrogen. However, before women reach menopause, most of their estrogen is made by their ovaries. And only a small amount is made by the aromatase enzyme.

While Arimidex stops the aromatase enzyme from working, it doesn’t stop your ovaries from making estrogen.

If you take Arimidex to treat breast cancer before you’ve reached menopause, you’ll also need to take treatment that stops your ovaries from making estrogen. This is typically done with a type of drug called a luteinizing hormone-releasing hormone (LHRH) analog. Treatment may also be done using radiation on your ovaries or by having surgery to remove your ovaries.

If you’d like to know more about using Arimidex for breast cancer before you’ve reached menopause, talk with your doctor.

Arimidex for ovarian cancer (off-label use)

Arimidex isn’t FDA-approved to treat ovarian cancer. However, the American Cancer Society notes that hormone therapy is sometimes used to treat a certain type of ovarian cancer called a stromal tumor. (Arimidex is considered a hormone therapy.) But keep in mind that this is an off-label use of the drug.

Stromal tumors start in tissue inside your ovaries that produces estrogen and progesterone. The hormone therapies that are sometimes used to treat this kind of cancer include aromatase inhibitors, such as Arimidex.

If you have questions about treatment options for ovarian cancer, talk with your doctor.

Arimidex for uterine cancer, including endometrial cancer (off-label use)

Arimidex isn’t FDA-approved to treat uterine cancer, including endometrial cancer. (Endometrial cancer affects the lining inside your uterus.)

However, the American Cancer Society notes that the drug may be helpful for women with either endometrial cancer or endometrial stromal sarcoma. (Endometrial stromal sarcoma affects the uterine lining, as well as the muscular wall of your uterus.) But keep in mind that these are off-label uses of Arimidex.

Most endometrial cancers are encouraged to grow by estrogen. First-line treatment of endometrial cancer is usually surgery that’s done to remove the uterus. The ovaries are often removed as well so that estrogen production is reduced.

But if these treatments don’t work to treat the endometrial cancer, a hormone therapy may be used to further reduce estrogen in your body. Hormone therapies, such as Arimidex, are typically used to treat endometrial cancers that are advanced or that have come back after a past treatment. Arimidex may also be helpful for women who can’t have surgery for their endometrial cancer.

If you have questions about treatment options for uterine cancer, talk with your doctor.

Arimidex for uterine fibroids (off-label use)

Arimidex isn’t FDA-approved to treat uterine fibroids. With this condition, you have noncancerous growths in your uterus.

However, Arimidex has been used off-label to reduce the size of fibroids and to help relieve pain that’s caused by them. The drug has also been given to reduce bleeding that’s caused by fibroids when other treatments haven’t worked.

If you have questions about using Arimidex for uterine fibroids, talk with your doctor. They can recommend safe and effective treatment options.

Arimidex for breast cancer prevention (off-label use)

Arimidex isn’t FDA-approved to prevent breast cancer. However, sometimes it’s used off-label to prevent breast cancer in certain women who are at high risk for the condition.

In fact, Arimidex is recommended in current guidelines for preventing breast cancer in certain women who are at high risk for developing breast cancer.

If you have questions about using Arimidex to prevent breast cancer, talk with your doctor.

Arimidex for bodybuilding (not a legal use)

Arimidex is sometimes used by bodybuilders and other athletes to offset certain side effects of anabolic steroids. However, the FDA has not approved this use, and buying Arimidex for this purpose is illegal. In addition, the World Anti-Doping Agency lists Arimidex as a substance that’s prohibited for use in competitive sports.

Arimidex and children

Arimidex isn’t FDA-approved for use in children.

The drug has been studied in boys ages 11 to 18 years with gynecomastia (breast growth in males). It’s also been studied in girls ages 2 to 9 years with early puberty that’s caused by McCune-Albright Syndrome. However, Arimidex wasn’t found to be effective for either of these conditions.

Depending on the type of breast cancer you’re using Arimidex to treat, you might take other drugs with Arimidex.

For example, Arimidex is sometimes taken with targeted therapies to treat advanced breast cancer. (With advanced breast cancer, the cancer has either spread to nearby areas or lymph nodes, called locally advanced breast cancer, or spread to other parts of your body, called metastatic breast cancer.)

Targeted therapies work on specific features of cancer cells. These therapies include drugs such as palbociclib (Ibrance) and ribociclib (Kisqali).

In addition, if you’re at risk for weakened bones with Arimidex treatment, you might take a medication called a bisphosphonate to help protect your bones. Examples of bisphosphonates include alendronate (Fosamax) and risedronate (Actonel). For more information about the risk of weakened bones with Arimidex treatment, see the section “Arimidex side effects” above.

If you’d like to know more about taking other drugs with Arimidex, talk with your doctor. They can recommend a treatment plan that’s right for you.

Other drugs are available that can treat breast cancer. Some may be a better fit for you than others. If you’re interested in finding an alternative to Arimidex, talk with your doctor. They can tell you about other medications that may work well for you.

Examples of other drugs that may be used to treat breast cancer include:

  • hormone therapies, other than Arimidex, such as:
    • tamoxifen (Soltamox)*
    • letrozole (Femara)*
    • exemestane (Aromasin)*
    • fulvestrant (Faslodex)
    • toremifene (Fareston)
  • targeted therapies, such as:
  • chemotherapy drugs, such as:
    • doxorubicin (Adriamycin)
    • epirubicin (Ellence)
    • paclitaxel (Abraxane)
    • docetaxel (Taxotere)
    • capecitabine (Xeloda)
    • cyclophosphamide

* These drugs are also used for adjuvant treatment of breast cancer. Adjuvant treatment is given to lower the risk of breast cancer coming back after it’s been treated with surgery.

You may wonder how Arimidex compares with other medications that are prescribed for similar uses. Here we look at how Arimidex and tamoxifen are alike and different.

Ingredients

Arimidex contains the active drug anastrozole. Tamoxifen is an active drug that’s available in both generic and brand-name forms. (A generic drug is an exact copy of the active drug in a brand-name medication.)

Arimidex and tamoxifen are both hormone therapies that are used to treat breast cancer. These drugs work by stopping the hormone estrogen from encouraging cancer cells to grow and spread.

Arimidex is a type of hormone therapy called an aromatase inhibitor. It works by stopping estrogen from being made in your body by the aromatase enzyme. On the other hand, tamoxifen is a type of hormone therapy called a selective estrogen receptor modulator (SERM). It works by stopping estrogen from attaching to cancer cells in your body.

Uses

Arimidex is approved to treat breast cancer in women who’ve gone through menopause. Specifically, Arimidex is used to treat the following types of breast cancer:

  • Early hormone receptor-positive (HR+) breast cancer. For this type of cancer, Arimidex is given to lower the risk of the breast cancer coming back or spreading after it’s already been treated with surgery. This type of treatment is called adjuvant treatment. (Early breast cancer hasn’t spread out of either your breast or the lymph nodes in your armpit. And HR+ cancer is stimulated to grow by hormones, including estrogen.)
  • Locally advanced or metastatic breast cancer that’s either HR+ or HR-unknown. Locally advanced or metastatic breast cancer typically can’t be treated with surgery. For these conditions, Arimidex is used as a first-line treatment. With first-line treatment, the drug is the first treatment used for the cancer. (Locally advanced breast cancer has spread to nearby areas or lymph nodes, while metastatic breast cancer has spread to other parts of your body. And while HR+ breast cancer is stimulated to grow by hormones, HR-unknown cancer may or may not be encouraged to grow by hormones.)
  • Locally advanced or metastatic breast cancer that’s come back or spread after treatment with the cancer drug tamoxifen. For this use, Arimidex can be given to treat HR+, HR-negative (HR–), or HR-unknown breast cancer. However, if your breast cancer is estrogen receptor-negative (ER–), or it didn’t improve with tamoxifen treatment in the past, it’s unlikely to improve with Arimidex. (ER– cancer doesn’t need estrogen in order to grow.)

Tamoxifen is approved for use in both men and women. In fact, it can be prescribed for all women, regardless of whether they’ve reached menopause. Tamoxifen is used to:

  • lower the risk of early estrogen receptor-positive (ER+) breast cancer from coming back or developing in the opposite breast after surgery (called adjuvant treatment)
  • treat ER+ metastatic breast cancer
  • lower the risk of invasive breast cancer (cancer that’s developed in the breast tissue or lymph nodes) after surgery and radiation treatment in women with ductal carcinoma in situ (DCIS)*
  • help prevent breast cancer in women who have high risk of developing the condition

* With DCIS, which is the earliest form of breast cancer, cancer cells are only found in your milk ducts.

Drug forms and administration

Arimidex comes as tablets that are taken by mouth once a day.

Tamoxifen comes as tablets that are taken by mouth either once or twice a day. Tamoxifen tablets used to be sold as the brand-name drug Nolvadex. However, this brand-name drug has been discontinued.

Tamoxifen is also available in a liquid form that’s sold as the brand-name drug Soltamox.

Side effects and risks

Arimidex and tamoxifen can cause some similar and some different side effects. Below are examples of these side effects.

Mild side effects

These lists contain examples of mild side effects that can occur with Arimidex, with tamoxifen, or with both drugs (when taken individually).

  • Can occur with Arimidex:
    • fatigue (lack of energy)
    • dizziness
    • pain, such as joint or back pain
    • rash
    • sore throat
    • weakness
    • nausea and vomiting
    • insomnia (trouble sleeping)
    • headache
    • bone pain
  • Can occur with tamoxifen:
    • vaginal discharge or bleeding
  • Can occur with both Arimidex and tamoxifen:
    • hot flashes
    • peripheral edema (swelling in your legs, ankles, or feet that’s caused by fluid retention)
    • lymphedema (buildup of lymphatic fluid in the tissues of your arm, which causes swelling in the area)
    • mood changes, such as depression

Serious side effects

These lists contain examples of serious side effects that can occur with Arimidex, with tamoxifen, or with both drugs (when taken individually).

  • Can occur with Arimidex:
    • skin reactions
    • reduced bone mineral density (weakened bones)
  • Can occur with tamoxifen:
    • blood clots in your veins or lungs*
    • stroke*
    • changes in the lining of your uterus that could lead to cancer in your uterus*
    • cataracts (cloudiness in the lens of your eye)
    • high calcium level in your blood
    • changes to your blood cell levels, such as low levels of either platelets or white blood cells
  • Can occur with both Arimidex and tamoxifen:
    • severe allergic reaction
    • liver problems, such as hepatitis (liver inflammation)

* Tamoxifen has a boxed warning for these side effects. A boxed warning is the most serious warning from the Food and Drug Administration (FDA).

Effectiveness

Arimidex and tamoxifen have different FDA-approved uses. But they’re both used in women who’ve gone through menopause as adjuvant treatment of early breast cancer and as treatment of advanced breast cancer.

In a clinical study of women with early breast cancer, 5 years of Arimidex treatment after surgery was more effective than 5 years of tamoxifen treatment after surgery for preventing:

  • their cancer from coming back after surgery
  • their cancer from spreading to other areas of their body
  • their cancer from occurring in their other (unaffected) breast
  • death

One study looked at treatment in women with advanced breast cancer. In this study, first-line treatment with Arimidex was more effective than first-line treatment with tamoxifen in slowing down the growth and spread of the women’s cancer. For this study, 88% of the women had HR+ cancer. The hormone receptor status wasn’t known in 11% of the women.

Costs

Arimidex is a brand-name drug. It’s also available in generic form. (A generic drug is an exact copy of the active drug in a brand-name medication.)

Tamoxifen is an active drug that’s available in both generic and brand-name forms.

According to estimates on GoodRx.com, brand-name Arimidex generally costs more than the generic drug tamoxifen costs. The actual price you’ll pay for either drug depends on your insurance plan, the dosage your doctor prescribes, your location, and the pharmacy you use.

You may wonder how Arimidex compares with other medications that are prescribed for similar uses. Here we look at how Arimidex and letrozole are alike and different.

Ingredients

Arimidex contains the active drug anastrozole. Letrozole is an active drug that’s available in both generic and brand-name forms. (A generic drug is an exact copy of the active drug in a brand-name medication.) For example, letrozole is sold as the brand-name drug Femara.

Arimidex and letrozole are both hormone therapies that are used to treat breast cancer. Hormone therapies for breast cancer work by stopping estrogen from encouraging the cancer to grow and spread. Both of these drugs belong to a class of drugs called aromatase inhibitors. (A class of drugs is a group of medications that work in a similar way.)

Uses

Arimidex and letrozole are approved to treat breast cancer in women who’ve gone through menopause. Specifically, these drugs are used to treat the following types of breast cancer:

  • Early hormone receptor-positive (HR+) breast cancer. For this type of cancer, Arimidex or letrozole is given to lower the risk of the breast cancer coming back or spreading after it’s already been treated with surgery. This type of treatment is called adjuvant treatment. (Early breast cancer hasn’t spread out of either your breast or the lymph nodes in your armpit. And HR+ cancer is stimulated to grow by hormones, including estrogen.)
  • Locally advanced or metastatic breast cancer that’s either HR+ or HR-unknown. Locally advanced or metastatic breast cancer typically can’t be treated with surgery. For these conditions, Arimidex or letrozole is used as a first-line treatment. With first-line treatment, the drug is the first treatment used for the cancer. (Locally advanced breast cancer has spread to nearby areas or lymph nodes, while metastatic breast cancer has spread to other parts of your body. And while HR+ breast cancer is stimulated to grow by hormones, HR-unknown cancer may or may not be encouraged to grow by hormones.)
  • Locally advanced or metastatic breast cancer that’s come back or spread after a past hormone treatment. (For Arimidex use, this past drug must have been tamoxifen.) For this use, either Arimidex or letrozole can be given to treat HR+, HR-negative (HR–), or HR-unknown breast cancer. However, if your breast cancer is estrogen receptor-negative (ER–), or it didn’t respond at all to tamoxifen treatment in the past, it’s unlikely to improve with Arimidex. (ER– cancer doesn’t need estrogen in order to grow.)

In addition, letrozole is also approved to lower the risk of early HR+ breast cancer from coming back after both surgery and 5 years of tamoxifen treatment. Arimidex is used off-label for this purpose. (With off-label use, a drug that’s approved for one purpose is used for another.)

Drug forms and administration

Both Arimidex and letrozole come as tablets that are taken by mouth once a day.

Side effects and risks

Arimidex and letrozole both contain a type of drug called an aromatase inhibitor. Therefore, these medications can cause very similar side effects. Below are examples of these side effects.

Mild side effects

These lists contain examples of mild side effects that can occur with Arimidex, with letrozole, or with both drugs (when taken individually).

  • Can occur with Arimidex:
    • rash
    • sore throat
    • back pain
    • nausea and vomiting
    • insomnia (trouble sleeping)
    • peripheral edema (swelling in your legs, ankles, or feet that’s caused by fluid retention)
    • lymphedema (buildup of lymphatic fluid in the tissues of your arm, which causes swelling in the area)
    • mood changes, such as depression
  • Can occur with letrozole:
    • no unique mild side effects
  • Can occur with both Arimidex and letrozole:
    • hot flashes
    • weakness
    • fatigue (lack of energy)
    • dizziness
    • pain, such as joint or bone pain
    • headache

Serious side effects

These lists contain examples of serious side effects that can occur with Arimidex, with letrozole, or with both drugs (when taken individually).

  • Can occur with Arimidex:
    • liver problems, such as hepatitis (liver inflammation)
    • skin reactions
  • Can occur with letrozole:
    • no unique serious side effects
  • Can occur with both Arimidex and letrozole:
    • severe allergic reaction
    • reduced bone mineral density (weakened bones)

Effectiveness

Arimidex and letrozole are both FDA-approved for use in women who’ve gone through menopause. These drugs can be used for adjuvant treatment of early breast cancer and as treatment of advanced breast cancer.

One clinical study found Arimidex and letrozole to be similarly effective for adjuvant treatment of early breast cancer.

In addition, the American Cancer Society considers these drugs to be similarly effective for treating both early and advanced breast cancer.

Costs

Arimidex is a brand-name drug. It’s also available in generic form. (A generic drug is an exact copy of the active drug in a brand-name medication.)

Letrozole is an active drug that’s available in both generic and brand-name forms.

According to estimates on GoodRx.com, Arimidex costs significantly more than generic form letrozole costs. The actual price you’ll pay for either drug depends on your insurance plan, your location, and the pharmacy you use.

Here are answers to some frequently asked questions about Arimidex.

How much does Arimidex increase survival?

The survival rates after using certain hormone therapies for early breast cancer were looked at in one review of breast cancer studies. (With early breast cancer, the cancer hasn’t spread out of either your breast or the lymph nodes in your armpit.)

According to this review, taking an aromatase inhibitor, such as Arimidex, for 5 years reduced the risk of dying from breast cancer within the following 5 years by 40%. This means that people taking an aromatase inhibitor for 5 years have a 40% lower risk of death from breast cancer compared with people using no hormone treatment.

If you have questions about survival rates for people taking Arimidex, talk with your doctor. And keep in mind that results of Arimidex treatment may vary from person to person.

What happens when you stop taking Arimidex?

When you stop taking Arimidex, the drug that’s left in your body will be gradually broken down by your liver. How long Arimidex stays in your system can vary from person to person. But most of the drug is usually removed from your body within about 10 days.

While in your body, Arimidex works to lower your estrogen level. This hormone level will stay low for up to 6 days after you’ve stopped taking the drug. This is the period of time until your body starts to gradually begin making estrogen again.

If you had side effects related to low estrogen, such as hot flashes, these should start to lessen as your estrogen level increases.

Stopping Arimidex doesn’t cause withdrawal symptoms. (Withdrawal symptoms are side effects that can happen when you stop taking a drug that your body is relying upon.) And stopping Arimidex suddenly (sometimes called “stopping cold turkey”) shouldn’t cause any problems for you.

If you’ve been taking Arimidex to lower the risk of your breast cancer coming back, studies show that your risk is still lowered for at least 5 years after you stop treatment. (This applies to people who’ve taken Arimidex for about 5 years of treatment.)

If you’re thinking about stopping Arimidex, talk with your doctor. They can discuss with you the risks and benefits of doing so.

How much does Arimidex lower your estrogen?

Arimidex can lower your estrogen level by about 70% after 24 hours following your dose of the drug. The level will typically be lowered by about 80% after you’ve taken Arimidex every day for 2 weeks. Your estrogen level may stay this low for up to 6 days after you stop taking Arimidex.

Will I have any permanent damage after using Arimidex?

It’s not likely that you will. In fact, side effects of Arimidex usually go away once you’ve stopped taking the drug.

However, Arimidex can weaken your bones while you’re taking it. And some women can develop osteoporosis from this. (With osteoporosis, you have thin, weak bones.) You also have an increased risk of breaking a bone with Arimidex treatment. But one study found that after stopping Arimidex, the risk of breaking a bone was no longer increased.

If you’re concerned about long-term side effects or permanent damage caused by Arimidex, talk with your doctor. They can discuss with you the risks and benefits of using this drug.

What percentage of people have breast cancer recurrence while they’re taking Arimidex?

Like all drugs, Arimidex doesn’t work for everyone. And this drug is less likely to prevent breast cancer recurrence if your cancer is estrogen receptor-negative (ER–). (ER– cancer doesn’t need estrogen in order to grow.)

One clinical study looked at Arimidex as adjuvant treatment for breast cancer in women who were postmenopausal. (For adjuvant treatment, Arimidex is given to lower the risk of the breast cancer coming back or spreading, after it’s already been treated with surgery.)

In this study, breast cancer did come back in some people. It came back either in the same breast, in the other breast, or in another part of their body.

Over this 5-year study, breast cancer came back in 10.4% of women who took Arimidex. In comparison, breast cancer came back in 12% of women who took the cancer drug tamoxifen for adjuvant treatment.

Out of the women whose breast cancer was hormone receptor-positive (HR+),* cancer came back in 8.6% of women who took Arimidex. In comparison, of those with HR+ breast cancer who took tamoxifen, up to 10.2% had their cancer come back.

* With HR+, the cancer is stimulated to grow by hormones, including estrogen.

Arimidex is approved to treat certain types of breast cancer in women who’ve gone through menopause.

What breast cancer is

Breast cancer develops when cells in your breast start to grow and multiply (make more cells) more quickly than usual. With most breast cancers, the abnormal cells are encouraged to grow by the hormone estrogen.

If your breast cancer is stimulated by hormones, such as estrogen, certain tests will show that the cancer cells have receptors (attachment sites) for those hormones. This type of breast cancer is called hormone receptor-positive (HR+).

HR+ cancers can be treated with hormone therapies that lower the estrogen level in your body. And because most breast cancer is HR+, hormone therapies are also sometimes used to treat breast cancer whose receptor status isn’t known.

What Arimidex does

Arimidex is a hormone therapy that’s used to treat certain forms of breast cancer. It’s a type of drug called an aromatase inhibitor. Arimidex works by stopping (inhibiting) the action of an enzyme called aromatase. (Enzymes are certain proteins that help chemical reactions to happen inside your body.)

The aromatase enzyme makes estrogen out of steroid hormones in your body, such as testosterone. Aromatase is found in various tissues, including your brain, fat, and skin.

Before menopause, estrogen is mainly produced by your ovaries. And just a small amount is made by the aromatase enzyme. But after menopause, your ovaries stop producing estrogen. At that point, the aromatase enzyme is the main way that your body makes estrogen. (And in men, estrogen is also mainly produced by the aromatase enzyme.)

By stopping aromatase from working, Arimidex lowers the amount of estrogen in your body. This helps to stop estrogen from encouraging breast cancer to grow and spread.

How long does it take to work?

Arimidex will start working soon after you begin taking it. But you won’t be able to notice this. Your doctor may order different kinds of tests during your treatment to check and see if the drug is working for you.

Alcohol isn’t known to interact with Arimidex. However, if you have certain side effects of Arimidex, drinking alcohol could worsen them. These side effects include headaches, dizziness, nausea, and tiredness.

Drinking large amounts of alcohol while you’re taking Arimidex can increase your risk of osteoporosis (weak, thin bones). Because of this risk, it’s best to avoid drinking large amounts of alcohol during Arimidex treatment.

Drinking alcohol is also known to raise your risk of developing breast cancer. But at this time, it’s not known if drinking alcohol after you’re diagnosed with breast cancer can make your cancer worse or make it more likely to come back after treatment.

If you drink alcohol and you’re concerned about how this could affect your breast cancer or its treatment, talk with your doctor. They can give you advice on much alcohol is safe for you to drink.

Arimidex can interact with several other medications.

Different interactions can cause different effects. For instance, some interactions can interfere with how well a drug works. Other interactions can increase side effects or make them more severe.

Arimidex and other medications

Below are lists of medications that can interact with Arimidex. These lists do not contain all the drugs that may interact with Arimidex.

Before taking Arimidex, talk with your doctor and pharmacist. Tell them about all prescription, over-the-counter, and other drugs you take. Also tell them about any vitamins, herbs, and supplements you use. Sharing this information can help you avoid potential interactions.

If you have questions about drug interactions that may affect you, ask your doctor or pharmacist.

Arimidex and tamoxifen

Like Arimidex, tamoxifen is a hormone therapy that’s used to treat breast cancer. But taking tamoxifen with Arimidex can lower the amount of Arimidex in your body. This can make Arimidex less effective for you.

Because of this interaction, you shouldn’t take tamoxifen with Arimidex. However, if recommended by your doctor, it’s fine to take Arimidex after you’ve finished taking tamoxifen.

Arimidex and drugs that contain estrogen

Taking Arimidex with drugs that contain estrogen could make Arimidex less effective for you. Because of this, you shouldn’t take these types of drugs while you’re using Arimidex.

Examples of drugs that contain estrogen include:

If you have questions about using medications that contain estrogen with Arimidex, talk with your doctor.

Arimidex and herbs and supplements

There aren’t any herbs or supplements that have been specifically reported to interact with Arimidex. However, you should still check with your doctor or pharmacist before using any of these products while taking Arimidex.

For example, it’s possible that supplements such as red clover or wild yam could make Arimidex less effective. (These supplements are used by some women to reduce menopausal symptoms, such as hot flashes.)

This interaction is possible because these supplements contain phytoestrogens, which are weak estrogen-like substances found in certain plants. There isn’t enough information available to say for sure whether taking phytoestrogens can affect your breast cancer treatment or not.

Be sure to talk with your doctor before taking any herbs or supplements with Arimidex.

Arimidex and foods

There aren’t any foods that are known to interact with Arimidex. Talk with your doctor to find out if there are any foods you should avoid during Arimidex treatment.

The side effects of taking too much Arimidex might include an increase in some of the typical side effects of the drug. However, in some clinical studies Arimidex was given at a dosage of 10 mg daily, which is higher than the recommended dosage. And people taking this dosage didn’t have additional or more severe side effects than did people taking a lower dosage of the drug.

If you accidentally took two Arimidex tablets instead of just one, it would be unlikely that you’d have any serious problems.

However, do not use more Arimidex than your doctor recommends. It’s not known if there is a dosage of Arimidex that could cause a life threatening overdose.

What to do in case of overdose

If you think you’ve taken too much of this drug, call your doctor. You can also call the American Association of Poison Control Centers at 800-222-1222 or use their online tool. But if your symptoms are severe, call 911 or go to the nearest emergency room right away.

You should take Arimidex according to your doctor’s or healthcare provider’s instructions.

When to take

You can take your Arimidex dose at any time of the day. But try to stick with the same time each day.

To help make sure that you don’t miss a dose, try setting a reminder on your phone. A medication timer may be useful, too.

Taking Arimidex with food

You can take Arimidex either with or without food.

Can Arimidex be crushed, split, or chewed?

No, you shouldn’t crush, split, or chew Arimidex tablets. Instead, you should swallow them whole. If you have trouble swallowing pills, talk with your doctor or pharmacist.

When you get Arimidex from the pharmacy, the pharmacist will add an expiration date to the label on the bottle. This date is typically 1 year from the date they dispensed the medication.

The expiration date helps guarantee that the medication is effective during this time. The current stance of the Food and Drug Administration (FDA) is to avoid using expired medications. If you have unused medication that has gone past the expiration date, talk to your pharmacist about whether you might still be able to use it.

Storage

How long a medication remains good can depend on many factors, including how and where you store the medication.

Arimidex tablets should be stored at room temperature (68°F to 77°F/20°C to 25°C) in a tightly sealed container. Avoid storing this medication in areas where it could get damp or wet, such as in bathrooms.

Disposal

If you no longer need to take Arimidex and have leftover medication, it’s important to dispose of it safely. This helps prevent others, including children and pets, from taking the drug by accident. It also helps keep the drug from harming the environment.

The FDA website provides several useful tips on medication disposal. You can also ask your pharmacist for information on how to dispose of your medication.

As with all medications, the cost of Arimidex can vary.

The actual price you’ll pay depends on your insurance plan, your location, and the pharmacy you use.

Your insurance plan may require you to get prior authorization before approving coverage for Arimidex. This means that your doctor and insurance company will need to communicate about your prescription before the insurance company will cover the drug. The insurance company will review the request and let you and your doctor know if your plan will cover Arimidex.

If you’re not sure if you’ll need to get prior authorization for Arimidex, contact your insurance company.

Financial and insurance assistance

If you need financial support to pay for Arimidex, or if you need help understanding your insurance coverage, help is available.

AstraZeneca, the manufacturer of Arimidex, offers a program called Arimidex Patient Direct, which can help to lower the cost of your prescription. This program also provides support from pharmacists.

For more information and to find out if you’re eligible for support, call 855-250-2483 or visit the program website.

Arimidex hasn’t been studied in pregnant women. In animal studies, the drug did cause harm to fetuses when it was given to pregnant females. Keep in mind that animal studies don’t always predict what will happen in humans. However, based on how Arimidex works, it could be harmful to a human fetus if taken during pregnancy.

Before starting Arimidex, tell your doctor if you’re pregnant or planning to become pregnant. And see your doctor right away if you get pregnant or think you could be pregnant while you’re taking Arimidex.

If you’re a female who’s able to become pregnant, your doctor will check for pregnancy before having you start Arimidex.

Arimidex could harm a fetus if taken during pregnancy. If you’re sexually active and you or your partner can become pregnant, talk with your doctor about your birth control needs while you’re using Arimidex.

If you’re a woman who’s able to become pregnant, you should use birth control while taking this drug. And you should continue using birth control for at least 3 weeks after your last dose of Arimidex.

It’s not known if Arimidex passes into human breast milk, or if it affects how your body makes breast milk. But the drug could be harmful to a child who consumes it in breast milk.

You shouldn’t breastfeed while using this drug, or for at least 2 weeks after taking your last dose.

If you’re breastfeeding, talk with your doctor before taking Arimidex. They can recommend safe and healthy ways to feed your child.

Before taking Arimidex, talk with your doctor about your health history. Arimidex may not be right for you if you have certain medical conditions or other factors affecting your health. These include:

  • Allergy to Arimidex. Don’t take Arimidex if you’re allergic to anastrozole (the active drug in Arimidex) or to any of the inactive ingredients in Arimidex. If you’re unsure about your medication allergies, talk with your doctor.
  • Ischemic heart disease. With this condition, the blood flow to your heart is lower than usual. This is due to narrowed arteries that supply blood to your heart. If you have angina (a type of chest pain) or you’ve ever had a heart attack, taking Arimidex could worsen your heart problems. Talk with your doctor about any heart issues before taking Arimidex. And call your doctor right away if you have new or worsening chest pain, or shortness of breath while you’re taking Arimidex.
  • High cholesterol levels. Arimidex can increase your cholesterol level. During Arimidex treatment, you’ll have blood tests to check your cholesterol level. If your level rises too high, your doctor may recommend medication to help lower your cholesterol.
  • Osteoporosis. Arimidex can weaken your bones. This can cause new or worsening osteoporosis (weak, thin bones). The drug also increases your risk of breaking a bone. Your doctor may want to measure your bone mineral density while you’re taking Arimidex. If you have osteoporosis, or any risk factors for developing this condition, you may need to take medication to help protect your bones during Arimidex treatment. (Risk factors for osteoporosis include having a family history of osteoporosis, inactivity, smoking, drinking alcohol, and not getting enough calcium or vitamin D.) Talk with your doctor about your risk for bone density loss while you’re taking Arimidex.
  • Severe liver problems. Arimidex hasn’t been studied in people with severe liver problems. Rarely, this drug may cause liver problems, such as hepatitis (liver inflammation). Let your doctor know if you’ve had any liver issues before taking Arimidex. Talk with your doctor about whether this drug is right for you.
  • Menstruation. If you’re still having periods (menstruating), talk with your doctor before taking Arimidex. The drug is approved for use only by women who are postmenopausal. (Being postmenopausal means that you’ve gone through menopause and no longer have periods.) If you’re still having periods, ask your doctor if treatments other than Arimidex are better choices for you.
  • Pregnancy. Arimidex may cause fetal harm if taken during pregnancy. For more information, please see the “Arimidex and pregnancy” section above.
  • Breastfeeding. Do not take Arimidex if you are breastfeeding. For more information, please see the “Arimidex and breastfeeding” section above.

Note: For more information about the potential negative effects of Arimidex, see the “Arimidex side effects” section above.

The following information is provided for clinicians and other healthcare professionals.

Indications

Arimidex is approved for use in postmenopausal women as:

  • adjuvant treatment of hormone receptor-positive (HR+) early breast cancer
  • first-line treatment of locally advanced or metastatic HR+ or HR-unknown breast cancer
  • second-line treatment of advanced breast cancer with disease progression following tamoxifen; however, estrogen receptor-negative (ER–) cancers and nonresponders to tamoxifen rarely respond to Arimidex

Mechanism of action

Arimidex contains the aromatase inhibitor anastrozole. It blocks the action of the aromatase enzyme, which then prevents the conversion of androgens into estrogen. In postmenopausal women, estrogen is primarily produced by the aromatase enzyme.

The growth and spread of ER+ breast cancer are stimulated through the action of estrogen on the cancer cells. Blocking aromatase in postmenopausal women lowers estrogen levels. This reduces the risk of early HR+ breast cancer recurrence and can slow the growth and spread of advanced HR+ breast cancers.

Pharmacokinetics and metabolism

Anastrozole is rapidly absorbed after oral administration. Maximum blood levels are reached within 2 hours of dosing on an empty stomach. Taking Arimidex with food delays absorption but does not affect the amount of drug absorbed.

Steady state concentration is reached after about 7 days of once-daily dosing. Plasma protein binding of anastrozole is 40%.

Anastrozole is primarily hepatically metabolized, with approximately 85% of the drug eliminated this way. Approximately 10% of the drug is cleared renally. Anastrozole has an average half-life of 50 hours.

Severe renal impairment reduces total clearance of anastrozole by about 10%, but no dose adjustment is needed.

The clearance of anastrozole is reduced by 30% in stable hepatic cirrhosis compared to normal hepatic function, but plasma levels remained within normal range. No dose adjustment is needed in stable hepatic cirrhosis. Arimidex hasn’t been studied in severe hepatic impairment.

Contraindications

Arimidex is contraindicated in people with known hypersensitivity to anastrozole or any of the excipients of Arimidex.

Storage

Store Arimidex at room temperature (68°F to 77°F/20°C to 25°C).

Disclaimer: Medical News Today has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.