Imatinib is a man-made drug currently used for the treatment of patients with certain types of leukaemia (most commonly chronic myeloid leukaemia) and a rare type of cancer known as gastro-intestinal stromal tumour (GIST). It may also be used to treat other types of cancers as part of a research trial.
- How it works
- How it is given
- Possible side effects
- Additional information
How it works
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 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 (CML) 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. Because it blocks the ‘grow’ signal, imatinib is known as a signal transductase inhibitor. The chemical it blocks is called tyrosine kinase and so imatinib is also known as a tyrosine kinase inhibitor. CancerBACUP’s section on chronic myeloid leukaemia contains more information on using imatinib to treat CML.
How it is given
Imatinib is normally given once daily. It is available as 100mg orange capsules and the usual dose is currently 400-600mg per day. The capsules 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.
Possible side effects
Each person’s reaction to a cancer drug is unique. Some people may have very few side effects, while others may experience more. We have outlined the most common side effects. However, we have not included those which are very rare and therefore extremely unlikely to affect you. If you notice any effects which 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 as follows.
Nausea This is usually mild. The nausea can be relieved with anti-sickness medicines, which your doctor can prescribe. It can also be reduced by taking the tablet after food.
Diarrhoea This can usually be easily controlled with anti-diarrhoea medication, but let your doctor know if it is severe or continues. It is important to drink plenty of fluids if you have diarrhoea.
Leg aches/cramps These can often be eased by taking mild painkillers, which your doctor can prescribe.
Swelling of the face and around the eyes This is fairly common and is not harmful although it can be upsetting. Drinking plenty of fluids can help. Many people gain weight due to the swelling and 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.
Watery eyes Imatinib can cause more tears to be produced, which can lead to watery eyes.
Itchy rash This may be relieved with anti-histamine tablets and skin lotion if your skin becomes dry.
Temporary reduction in the production of blood cells by the bone marrow This can result in anaemia, risk of bruising and bleeding and infection. Your blood count will be checked regularly to see how well your bone marrow is working.
If your temperature goes above 38°C (100.5°F) or you have unexplained bruising or bleeding, or you suddenly feel unwell even if you have a normal temperature, contact your doctor or the hospital straight away. The dose of imatinib may need to be lowered, or (very rarely) stopped, if a person’s bone marrow is not able to function at a safe level during treatment.
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.
Things to remember about imatinib capsules
- It is important to take your capsules at the right times. You must take them as directed by your doctor.
- Keep the capsules in a safe place where children cannot reach them as imatinib could harm them.
- If your doctor decides to stop the treatment, return any remaining capsules to the pharmacist. Do not flush them down the toilet or throw them away.
- If you forget to take a capsule 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 do 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;
- Oxford Textbook of Oncology (2nd edition). Souhami et al. Oxford University Press, 2002.
- Treatment of Cancer (4th edition). Sikora. Arnold, 2002.
For further references, please see the general bibliography.