Anastrozole (Arimidex)

Anastrozole is also called Arimidex. It is a type of hormone therapy called an aromatase inhibitor and is used to treat breast cancer.

Many breast cancers are stimulated to grow by the female sex hormones oestrogen and progesterone. These breast cancers are called ‘hormone sensitive’ or ‘hormone receptor positive’ and can be treated with drugs that block the effects of these hormones. Although it is not understood why, some oestrogen receptor negative breast cancers can also be controlled by anastrozole.

Although women past their menopause don’t produce oestrogen from their ovaries, they still produce a small amount by turning other sex hormones (androgens) into oestrogen. Androgens are made by your adrenal glands, these are the small glands above your kidneys. Androgens need an enzyme called aromatase to turn them into oestrogen. This change happens mainly in fatty tissue, muscle and the skin. Aromatase inhibitors stop (inhibit) aromatase, so it can’t change the androgen into oestrogen.

These drugs are only suitable for women who've had their menopause. But some trials are looking into whether combining aromatase inhibitors with a drug called Zoladex can help some pre-menopausal women with breast cancer.

You take anastrozole as a tablet, once a day.  

It is very important that you take tablets according to the instructions your doctor or pharmacist gave you. Whether you have a full or empty stomach, for example, can affect how much of a drug gets into your bloodstream. You should take the right dose, not more or less. And never stop taking a cancer drug without talking to your specialist first.

We've listed the side effects associated with anastrozole below. You can use the links to find out more about each side effect. Where there is no link, please use the search box at the top of the page. Or look at the cancer drug side effects section.

Many women will have one or more of the following side effects

• Menopausal symptoms including hot flushes and sweats in more than 1 out of 10 (10%) women, and decreased interest in sex (reduced libido)
• Painful joints - this happens in about 1 out of 10 (10%) women 
• Tiredness or fatigue - this happens in about 1 in 10 (10%) of women
• Skin rashes in about 1 in 10 women (10%) - these are usually mild but you should let your doctor know if you have a rash
• Feeling or being sick happens in about 1 in 10 women (10%) - it is usually mild and can usually be controlled by anti-sickness medicines
• Headaches
• Painful hands with weakened grip and numbness and tingling - carpal tunnel syndrome

• Mood changes
• Cough and breathlessness - this affects less than 1 in 10 women (10%)
• Loss of bone density caused by a lack of oestrogen over a long period of time - the bones are weaker and more likely to break. You will have a 'DEXA scan' to check your bone density before you start treatment.
• Loss of appetite
• Increased level of cholesterol in the blood - this is usually only slightly raised and you will have regular blood tests to check it
• Hair thinning
• Diarrhoea - drink plenty of fluid and tell your doctor if diarrhoea becomes severe or continues for more than 3 days
• Dryness of the vagina
• Vaginal bleeding - this mainly happens when women have changed from one type of hormone therapy to another during the first few weeks of treatment. You should tell your doctor or nurse if the bleeding continues. This affects fewer than1 in 20 (5%) of women treated.

The side effects above may be mild or more severe. A side effect may get better or worse through your course of treatment, or more side effects may develop as the course goes on. This depends on

• How many times you've had the drug before
• Your general health
• The amount of the drug you have (the dose)
• Other drugs you are having

Talk to your doctor, pharmacist or nurse about all your side effects so that they can help you manage them. You should have a contact number for your chemotherapy nurse, clinic or ward nurse. You can ring if you have any questions or problems. They can give you advice or reassure you. If in doubt, call them.

Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and other over the counter remedies - some drugs can react together.