Anastrozole (Arimidex®)

This information is about a hormonal therapy called anastrozole that is also commonly called Arimidex®. It is used to treat breast cancer. The information should ideally be read with our general information about breast cancer| or secondary breast cancer. 

Arimidex Back To Top

Arimidex is a type of hormonal therapy used in the treatment of breast cancer in women who have had their menopause (change of life).

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.

There are several different types of hormonal therapy. Your doctor can discuss with you which is best for your particular situation.

Aromatase inhibitors Back To Top

Many breast cancers need supplies of the hormone oestrogen to grow. 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, known as aromatisation, happens mainly in the fatty tissues of the body.

Drugs that block the process of aromatisation, and so reduce the amount of oestrogen in the body, are known as aromatase inhibitors. Other aromatase inhibitors include; Femara® (letrozole)| and Aromasin® (exemestane)|.

How Arimidex is taken Back To Top

Arimidex is a tablet which is taken once a day. It should be swallowed whole with a glass of water. Take it at about the same time each day (it doesn't matter whether this is in the morning or evening).

When it may be given Back To Top

Doctors take into account many different factors when planning each person's treatment, so it is important to talk things over with your specialist. They will make a decision about treatment based on current medical knowledge and your individual situation. 

Early breast cancer

Arimidex can be used to treat post-menopausal women with early breast cancer (cancer that has not spread) after they have had surgery to remove the cancer. Giving treatment after surgery is known as adjuvant therapy.

Results from recent research studies suggest that for some women Arimidex may be more effective than tamoxifen, and that it has different side effects. It has also been shown that switching to Arimidex after taking tamoxifen for 2–3 years may be better than five years of tamoxifen for some women.

The National Institute for Health and Clinical Excellence (NICE)| advise doctors on the prevention and treatment of ill-health, and have produced guidance on the use of aromatase inhibitors in early breast cancer. The guidelines currently recommend that an aromatase inhibitor, such as Arimidex, should be considered as an adjuvant treatment for all women with early breast cancer. The choice about which hormonal therapy to use should be made following discussion between the doctor and the patient, and should include information about the potential risks and benefits of the treatment.

Advanced breast cancer

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

Possible side effects Back To Top

Each person's reaction to any medication is different. Most people have very few side effects with Arimidex, while others may experience more. The side effects described in this factsheet will not affect everyone and may be different if you are taking more than one drug.

We have outlined the most common side effects. However, we have not included those that are very rare and therefore extremely unlikely to affect you. If you notice any effects that are not listed in this information, please discuss them with your doctor or nurse.

You will see your doctor regularly while you have this treatment so that they can monitor the effects. This information should help you to discuss any queries about your treatment and its side effects with your doctor or nurse, as they are in the best position to help and advise you.

Some people may have 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 women find that avoiding or cutting down on tea, coffee, nicotine and alcohol can reduce sweats. Recent research suggests that progestogen or some anti-depressants may be helpful in controlling this side effect. Your doctor or nurse can discuss this with you.

Some women find that complementary therapies| help, and your GP may be able to give you details about getting these on the NHS.

If you are having troublesome hot flushes, discuss these with your doctor.

Vaginal dryness This may occur while using Arimidex. Gels that can help to overcome the dryness are available. The gels can be bought from any chemist or can be prescribed by your doctor.

Feeling sick (nausea), being sick (vomiting) and diarrhoea These side effects are rare. If they occur 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. 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 whilst taking Arimidex but this is not common. It is important to drink plenty of fluids. Let your doctor know if you are getting headaches, as they can prescribe medication.

Skin rashes Rarely, Arimidex can cause skin rashes.

Vaginal bleeding Vaginal bleeding (usually in the first few weeks of treatment) has been reported. This is rare and has usually occurred 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 troublesome. It may be 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 take extra care when driving or operating machinery.

Risk of osteoporosis Women who have osteoporosis (weakened bones) or are at risk of it, should have their bone strength assessed before and during treatment with Arimidex. In some situations it may be necessary to start treatment to help prevent osteoporosis from developing.

Length of treatment Back To Top

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

Things to remember about Arimidex tablets Back To Top

Arimidex may interact with other medicines. Let your doctor know 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 where children cannot reach them, as Arimidex could harm them.
• Arimidex tablets should be stored in the original packaging. They should be kept at room temperature away from direct heat and light.
• 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.
• If you are sick just after taking the tablet tell your doctor or nurse, as you may need to take another one.
• Remember to get a new prescription a few weeks before you run out of tablets, and make sure that you have plenty for holidays.

References Back To Top

This section has been compiled using information from a number of reliable sources, including:

• Martindale: The Complete Drug Reference (35th edition). Sweetman et al. Pharmaceutical Press, 2007.
• British National Formulary (54th edition). British Medical Association and Royal Pharmaceutical Society of Great Britain, September 2007.

For further references, please see the general bibliography|.