Idelalisib (Zydelig) | Cancer Research UK
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What idelalisib is

Idelalisib is pronounced eye-dell-al-iss-ib. It is also called by its brand name Zydelig.  It is a type of biological therapy.

Idelalisib is a treatment for

  • Chronic lymphocytic leukaemia (CLL) with another cancer drug called rituximab (Mabthera)
  • Follicular non Hodgkin lymphoma (NHL)

Idelalisib is used for CLL if your leukaemia is no longer responding to other treatments and has come back within 2 years. Or you may have it as a first treatment if your CLL has specific gene changes known as 17p deletion or TP53 mutation.

You might have idelalisib for NHL if you have had at least 2 other types of treatment and they are no longer working.

You may also have it as part of clinical trials for other types of cancer.


How idelalisib works

This type of drug works by blocking particular proteins inside cancer cells that encourage the cancer to grow. Idelalisib blocks a protein called PI3K and is called a PI3K inhibitor. Some lymphoma and leukaemia cells have too much PI3K. By blocking this protein, idelalisib may shrink the cancer or stop it growing for a time.


How you have idelalisib

You take idelalisib as a tablet twice a day. You can take it with or without food. Don’t chew or crush the tablet. You should swallow it whole with a glass of water.

It is very important that you take the tablets according to the instructions your doctor or pharmacist gives you. For example, whether you have a full or empty stomach can affect how much of a drug gets into your bloodstream. So check the pack leaflet and follow the instructions it gives. You should take the right dose, not more or less. And never stop taking a cancer drug without talking to your specialist first.

You usually carry on taking idelalisib for as long as it is working.


Common side effects

More than 10 in every 100 people have one or more of these side effects.

  • An increased risk of getting an infection from a drop in white blood cells – it is harder to fight infections and you can become very ill. You may have headaches, aching muscles, a cough, a sore throat, pain passing urine, or you may feel cold and shivery. If you have a severe infection this can be life threatening. Contact your treatment centre straight away if you have any of these effects or if your temperature goes above 38°C. You will have regular blood tests to check your blood cell levels
  • Bruising more easily due to a drop in platelets – you may have nosebleeds, bleeding gums after brushing your teeth, or lots of tiny red spots or bruises on your arms or legs (known as petechia)
  • Tiredness and breathlessness from a drop in red blood cells (anaemia). You may need a blood transfusion
  • Diarrhoea affects 4 out of 10 people (40%). It can start up to several months after you start treatment. Drink plenty and tell your doctor or nurse if you are worried about how bad it is, or if it continues for more than 3 days  
  • Skin changes happen in about 1 out of 4 people (25%). You may have a rash or red, dry, itchy skin
  • A raised temperature occurs in 1 in 5 people (20%)
  • Liver and heart changes that are very mild and unlikely to cause symptoms. They will almost certainly go back to normal when treatment is finished. Your doctor may stop treatment for a short time and may lower the dose. You will have regular blood tests to check how well your liver and heart are working
  • Lung inflammation, chest infection (pneumonia) and cough affects about 1 in 5 people (20%)
  • Feeling or being sick is usually well controlled with anti sickness medicines
  • Headaches
  • Loss of appetite
  • Mild effects on the liver which are unlikely to cause any symptoms. These will usually go back to normal after the treatment ends. You will have regular blood tests to check how your liver is working
  • Loss of fertility – you may not be able to become pregnant or father a child after this treatment. Talk to your doctor before starting treatment if you think you may want to have a baby in the future. Men may be able to store sperm before starting treatment

Occasional side effects

Between 1 and 10 in every 100 people have one or more of these side effects.


Rare side effects

Fewer than 1 in 100 people have a split in the wall of the bowel (bowel perforation) but this is a serious side effect if it happens.


Important points to remember

You may have some of the side effects listed above. They may be mild or more severe. The side effects may be different if you are also having other cancer drugs.

A side effect may get better or worse through your course of treatment. Or you may have more side effects as the course goes on. This depends on

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

Tell your doctor or nurse straight away if you are worried about any of the side effects or if they are severe.

Coping with side effects

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

Other medicines and foods

It is very important to tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and over the counter remedies. Many other medicines and herbal supplements can react with idelalisib.

In particular medicines, foods and herbal supplements which contain CYP enzymes can interfere with how idelalisib works.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having treatment with this drug and for a few months afterwards. Talk to your doctor or nurse about effective contraception before starting treatment.


Breastfeeding is not advisable during this treatment because the drug may come through in the breast milk.

Possible long term effects

Idelalisib is a fairly new drug in cancer treatment. This means that there is limited information available at the moment about possible longer term effects that it may cause. Tell your doctor if you notice anything that is not normal for you.



You should not have immunisations with live vaccines while you are having this treatment or for at least 6 months afterwards. In the UK, these include rubella, mumps, measles (usually given together as MMR), BCG, yellow fever and Zostavax (shingles vaccine).

You can have other vaccines, but they may not give you as much protection as usual until your immune system has fully recovered from your treatment. It is safe to have the flu vaccine.

It is safe for you to be in contact with other people who've had live vaccines as injections. There can be problems with vaccines you take by mouth (oral vaccines), but not many people in the UK have these now. So there is usually no problem in being with any baby or child who has recently had any vaccination in the UK. You might need to make sure that you aren't in contact with anyone who has had oral polio, cholera or typhoid vaccination recently, particularly if you live abroad.


More information about idelalisib

We don’t list all the very rare side effects of this treatment that are very unlikely to affect you. For further information look at the Electronic Medicines Compendium website at

If you have a side effect we don’t list here and you think it may be due to this treatment, you can report it to the Medicines Health and Regulatory Authority (MHRA). Go to

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Updated: 22 December 2014