This information is about a drug called imatinib, which is also known as Glivec®. Imatinib is a man-made drug currently used for the treatment of patients with chronic myeloid leukaemia (CML), and a rare type of cancer known as gastrointestinal stromal tumour (GIST). It may also be used to treat other types of cancers as part of a research trial.

Imatinib works by blocking (inhibiting) signals within cancer cells and preventing a series of chemical reactions that cause the cell to grow and divide.

The growth of cells in our bodies is controlled by a group of chemicals called growth factors. These chemicals can attach themselves to special proteins on the surface of particular cells. This starts a series of chemical reactions within the cell which trigger it to grow and multiply. In people with chronic myeloid leukaemia or GIST, cells are produced which have a damaged receptor protein. This receptor sends out the grow-and-divide signal to the cells even when there is no growth factor present.

Imatinib identifies the faulty receptor and sticks to it, which prevents it from stimulating the cells to grow. Imatinib is known as a signal transductase inhibitor, because it blocks the 'grow' signal. The chemical it blocks is called tyrosine kinase, so imatinib is also known as a tyrosine kinase inhibitor.

Imatinib is normally given once daily. It is available as 100mg and 400mg tablets or capsules. The tablets should be taken with a meal and a large glass of water. Imatinib is usually taken for as long as patients are benefiting from it.

Each person’s reaction to a cancer drug is different. Some people may have very few side effects, while others may experience more. We have outlined the most common side effects. We have not included those that are very rare, and which are therefore extremely unlikely to affect you. If you notice any effects that you think may be due to the drug but are not listed here, please discuss them with your doctor or nurse.

The side effects of imatinib are generally mild or moderate. They often occur during the first month of treatment and may get better after this initial period. The most common side effects are listed below.

Feeling sick (nausea) This is usually mild. The nausea can be relieved with anti-sickness (anti-emetic) drugs, which your doctor can prescribe. It can also be reduced by taking the tablet after food.

Diarrhoea This can usually be controlled easily with anti-diarrhoea medication, but let your doctor know if it is severe or if it continues. It is important to drink plenty of fluids if you have diarrhoea.

Headaches Some people have headaches when taking imatinib. Let your doctor know if you get any headaches as painkillers can be given to help.

Leg aches/cramps These can often be eased by taking mild painkillers, which your doctor can prescribe.

Fluid retention This is fairly common and is not harmful, although it can be upsetting. Many people gain weight, or notice swelling around the eyes and ankles due to the retention of fluid. Diuretics (drugs which make you pass more urine) can help to get rid of some of the fluid, but often it settles of its own accord. Let your doctor know if you put on a lot of weight very quickly.

Visual disturbances Imatinib can cause pain in the eyes and deterioration of vision. It may also cause more tears to be produced, which can lead to watery eyes.

Itchy rash If your skin becomes dry, this may be relieved with antihistamine tablets and skin lotion.

Lowered resistance to infection Imatinib can reduce the production of white blood cells by the bone marrow, making you more prone to infection. Your blood cells will be monitored while you are taking imatinib.

Contact your doctor or the hospital straightaway if:

• your temperature goes above 38ºC (100.5ºF)
• you suddenly feel unwell (even with a normal temperature).

You will have a blood test before having more chemotherapy to make sure that your cells have recovered. Occasionally it may be necessary to delay your treatment if the number of blood cells (the blood count) is still low.

Bruising or bleeding Imatinib can reduce the production of platelets (which help the blood to clot). Let your doctor know if you have any unexplained bruising or bleeding.

Anaemia (low number of red blood cells) While having treatment with imatinib you may become anaemic. This may make you feel tired and breathless. You may need to have a transfusion of blood if the number of red blood cells becomes too low.

Loss of appetite A dietitian or specialist nurse at your hospital can give advice and tips on boosting appetite, coping with eating difficulties and maintaining weight.

Some medicines can be harmful to take when you are having imatinib. Always tell your doctor about any other medicine you are taking, including those bought over the counter and herbal medicines.

Contraception Little is known about the effects of imatinib on a developing foetus. Therefore, it is not advisable to become pregnant or father a child while taking this drug.

• It is important to take your tablets at the right times. You must take them as directed by your doctor.
• Keep the tablets in a safe place where children cannot reach them, as imatinib could harm them.
• If your doctor decides to stop the treatment, return any tablets you have to the pharmacist. Do not flush them down the toilet or throw them away.
• If you forget to take a tablet do not take a double dose. Tell your doctor and keep to your regular dose schedule.

If you have any questions about these or any other side effects talk to your doctor or nurse. It is important to let them know if you are having any symptoms or side effects that may be related to any treatment you are having.

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

• Gastro-intestinal stromal tumours (GIST) – imatinib. National Institute for Health and Clinical Excellence (NICE), October 2004
• Leukaemia (chronic myeloid) imatinib: Guidance. National Institute for Health and Clinical Excellence (NICE), October 2003
• 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.