Anastrozole (Arimidex®)

This information is about a hormonal therapy used to treat breast cancer called anastrozole, which is also called Arimidex®. Throughout this page we refer to it by its more commonly used name, Arimidex.

This information should ideally be read with our general information about breast cancer or secondary breast cancer.

Arimidex

Arimidex is a type of hormonal therapy used in the treatment of breast cancer in women who have been through the menopause (change of life). You will see your doctor regularly while you have this treatment so they can monitor its effects.

Hormonal therapies interfere with the production or action of particular hormones in the body. Hormones are substances produced naturally in the body. They act as chemical messengers and help to control the activity of cells and organs. 

Aromatase inhibitors

Many breast cancers rely on the hormone oestrogen to grow. These cancers are known as hormone-sensitive breast cancers. In women who have had their menopause, the main source of oestrogen is through the conversion of androgens (sex hormones produced by the adrenal glands) into oestrogens. This is carried out by an enzyme called aromatase. The conversion process is known as aromatisation, and happens mainly in the fatty tissues of the body.

Arimidex is a drug that blocks the process of aromatisation, and so reduces the amount of oestrogen in the body. As less oestrogen reaches the cancer cells, they grow more slowly or stop growing altogether. Drugs that work in this way are known as aromatase inhibitors. Other aromatase inhibitors include letrozole (Femara®) and exemestane (Aromasin®).

How Arimidex is taken

Arimidex is a tablet which is taken 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.

When it is given

Your doctor will take into account a number of different factors when planning your treatment.

Arimidex is used to treat post-menopausal women with hormone-sensitive breast cancer.

Early breast cancer

Arimidex may be given to women with early breast cancer (cancer that has not spread) after they have had surgery to remove the cancer. Giving treatment after surgery, to reduce the chance of the cancer coming back, is known as adjuvant therapy.

For some women Arimidex may be more effective than tamoxifen, and it has different side effects. Studies show that switching to Arimidex after taking tamoxifen for 2–3 years may be better than five years of tamoxifen for some women. 

Advanced breast cancer

Arimidex can be used to treat women who have breast cancer that has spread to other parts of the body (advanced or secondary breast cancer). It can also be used to treat women whose breast cancer has come back after initial treatment.

Length of treatment

Your doctors will discuss the length of treatment that they feel is appropriate for you. Arimidex may be given over a number of years, or for as long as it is controlling your cancer, depending on your individual situation.

Possible side effects

Each person's reaction to any medicine is different. Most people have very few side effects with Arimidex, while others may experience more. The side effects described here won't affect everyone and may be different if you are taking more than one drug.

We have outlined the most common side effects, but haven't included those that are rare and therefore unlikely to affect you. If you notice any effects which aren't listed here, discuss them with your doctor or nurse.

You may have some of the following side effects, to varying degrees:

• Hot flushes and sweats These are usually mild and may wear off after a period of time. Sometimes people find it helps to cut down on tea, coffee, nicotine and alcohol. Research suggests that hormones called progestogens or some types of antidepressants may be helpful in controlling this side effect. Your doctor or nurse can discuss this with you.
  Some people find complementary therapies, such as acupuncture, helpful. Your GP may be able to give you details about having these on the NHS. If you find your own therapist, make sure that they are properly qualified and registered.
  You can read more about treatments like hot flushes in our information aboutbreast cancer treatment and menopausal symptoms  .     
• Vaginal dryness This may occur while using Arimidex. Gels that can help to overcome the dryness are available. You can buy these from a chemist or your doctor can prescribe them.
• Feeling sick (nausea) and being sick (vomiting) These side effects are rare and usually mild. They can usually be effectively treated, so let your doctor know.Feeling sick can often be relieved by taking your tablet with food or at night.
• Diarrhoea If you have diarrhoea it is important to drink plenty of fluids.
• Hair thinning Some women notice that their hair becomes thinner while taking Arimidex. This is usually mild and the hair regrows at the end of treatment.
• Headaches Some people have headaches while taking Arimidex, but this is not common. It's important to drink plenty of fluids. Let your doctor know if you are getting headaches, as they can prescribe medication to help.
• Skin rashes Rarely, Arimidex can cause skin rashes.
• Vaginal bleeding Some women have some vaginal bleeding, usually in the first few weeks of treatment. This is rare and usually occurs after changing from other hormonal therapies to treatment with Arimidex. If the bleeding continues, tell your doctor or breast care nurse.
• Joint pains/muscular stiffness Some women have pain and stiffness in their joints while taking Arimidex. Let your doctor know if these effects are a problem. You may find it helpful to take mild painkillers.
• Tiredness and lethargy Some people can have increased tiredness, especially at the start of treatment. It is important to get plenty of rest. If you are very sleepy you should not drive or operate machinery.
• Risk of osteoporosis Women who have, or are at risk of, osteoporosis (weakened bones), should have their bone strength assessed before and during treatment with Arimidex. Some women may need to take bone-strengthening drugs to help prevent osteoporosis developing.

Always let your doctor or nurse know about any side effects you have. There are usually ways in which they can be controlled or improved.

Things to remember about Arimidex tablets

• Arimidex may interact with other medicines. Tell your doctor about any medicines you are taking, including non-prescribed drugs such as complementary therapies, vitamins and herbal drugs.
• Keep the tablets in a safe place, out of the reach of children.
• Keep the tablets in the original packaging and store them at room temperature, away from heat and direct sunlight.
• Don't worry if you forget to take your tablet. Do not take a double dose. The levels of the drug in your blood will not change very much, but try not to miss more than one or two tablets in a row.
• If your doctor decides to stop the treatment, return any remaining tablets to the pharmacist. Do not flush them down the toilet or throw them away.
• Remember to get a new prescription a few weeks before you run out of tablets, and make sure that you have plenty for holidays.