Cytarabine (Ara C, cytosine arabinoside)

Cytarabine is a type of chemotherapy. It is also known as Ara C or cytosine arabinoside.

You pronounce cytarabine sye-ta-ra-bin.

It is a treatment for:

  • acute leukaemias (cancers of the blood)
  • some lymphomas (cancers of the lymph glands)

How does cytarabine work?

Cytarabine is a type of chemotherapy drug called an antimetabolite Open a glossary item.  It kills cancer cells by stopping them from making and repairing DNA that they need to grow and multiply.

How do you have cytarabine?

How you have cytarabine depends on what type of cancer you have. You can have it as an injection:

  • into your bloodstream (intravenously)
  • just under the skin (subcutaneously)
  • into your spinal fluid (intrathecal injection)

What is this information about?

This information is about having cytarabine into the bloodstream or as an injection under the skin.

Into your bloodstream

You might have treatment through a long plastic tube that goes into a large vein in your chest. The tube stays in place throughout the course of treatment. This can be a:

  • central line
  • PICC line
  • portacath

If you don't have a central line

You might have treatment through a thin short tube (a cannula) that goes into a vein in your arm. You have a new cannula each time you have treatment.

Injection under your skin

You usually have injections under the skin (subcutaneous injection) into the stomach, thigh or top of your arm. You might have stinging or a dull ache for a short time after this type of injection. The skin in the area may go red and itchy for a while.

Chemotherapy into the spinal fluid (intrathecal chemotherapy)

You might have chemotherapy injected into the fluid around the spinal cord (cerebrospinal fluid or CSF). This is called intrathecal chemotherapy. 

Your doctor gives you the drug during a procedure called lumbar puncture. The drug mixes with the cerebrospinal fluid and circulates through the brain.

When do you have cytarabine?

You usually have cytarabine as a course of several cycles of treatment. A cycle of treatment means that you have this drug and then have a rest to allow your body to recover. You usually have it with other drugs in your cycle.

Each cycle varies depending on what type of cancer you have. Your doctor or nurse will tell you more about this. 


You have blood tests before and during your treatment. They check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.

What are the side effects of cytarabine?

Side effects can vary from person to person. They also depend on what other treatments you're having. 

When to contact your team

Your doctor, nurse or pharmacist will go through the possible side effects. They will monitor you during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:

  • you have severe side effects 

  • your side effects aren’t getting any better

  • your side effects are getting worse

Early treatment can help manage side effects better. 

Contact your advice line immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

We haven't listed all the side effects here. Remember it is very unlikely that you will have all of these side effects. But you might have some of them at the same time.

You might have additional side effects if you are having high dose cytarabine. These additional side effects have been listed separately. Talk to your doctor, nurse or pharmacist to find out if you are having high dose treatment.

Common side effects

Each of these effects happens in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:

Increased risk of getting an infection

Increased risk of getting an infection is due to a drop in white blood cells. Symptoms include a change in temperature, aching muscles, headaches, feeling cold and shivery and generally unwell. You might have other symptoms depending on where the infection is.

Infections can sometimes be life threatening. You should contact your advice line urgently if you think you have an infection. 

Breathlessness and looking pale

You might be breathless and look pale due to a drop in red blood cells. This is called anaemia.

Bruising, bleeding gums or nosebleeds

This is due to a drop in the number of platelets in your blood. These blood cells help the blood to clot when we cut ourselves. You may have nosebleeds or bleeding gums after brushing your teeth. Or you may have lots of tiny red spots or bruises on your arms or legs (known as petechiae).

Sore mouth

Mouth sores and ulcers can be painful. It helps to keep your mouth and teeth clean, drink plenty of fluids and avoid acidic foods such as lemons. Chewing gum can help to keep your mouth moist. Tell your doctor or nurse if you have ulcers.


Contact your advice line if you have diarrhoea. For example, 2 or more extra loose bowel movements than usual each day. If you have a stoma, you might have more output than normal. Your doctor may give you anti diarrhoea medicine to take home with you after treatment.

Try to eat small meals and snacks regularly. It’s best to try to have a healthy balanced diet if you can. You don’t necessarily need to stop eating foods that contain fibre. But if your diet is normally very high in fibre, it might help to cut back on high fibre foods such as beans, nuts, seeds, dried fruit, bran and raw vegetables. 

Drink plenty to try and replace the fluid lost. Aim for 8 to 10 glasses per day.

Feeling or being sick

Feeling or being sick is usually well controlled with anti sickness medicines. It might help to avoid fatty or fried foods, eat small meals and snacks and take regular sips of water. Relaxation techniques might also help.

It is important to take anti sickness medicines as prescribed even if you don’t feel sick. It is easier to prevent sickness rather than treat it once it has started.

Tummy (abdominal) pain

Tell your treatment team if you have this. They can check the cause and give you medicine to help. 

Inflammation and ulcers of the opening at the end of the bowel (anus)

Talk to the team looking after you about this. They might be able to give you medicines or creams to help with this.

Liver changes

You might have liver changes that are usually mild and unlikely to cause symptoms. They usually go back to normal when treatment finishes. You have regular blood tests to check for any changes in the way your liver is working.

Hair loss

You could lose all your hair. This includes your eyelashes, eyebrows, underarms, legs and sometimes pubic hair. Your hair will usually grow back once treatment has finished but it is likely to be softer. It may grow back a different colour or be curlier than before. 

Skin rash

You might notice skin changes, such as dryness, itching, freckles and rashes similar to acne on your face, neck and trunk. 

Tell your doctor if you have any rashes or itching. Don't go swimming if you have a rash because the chlorine in the water can make it worse.

If your skin gets dry or itchy, using unperfumed moisturising cream may help. Check with your doctor or nurse before using any creams or lotions. Wear a high factor sun block if you’re going out in the sun.

High temperature 

Talk to the team looking after you or telephone your advice line.

Breathlessness and cough

Tell your doctor or nurse if you’re breathless or have a cough. This could be due to an infection, such as pneumonia. Or it could be caused by changes to the lung tissue, making it less flexible.

Contact your advice line if you are worried. You may need a course of antibiotics.

Cytarabine syndrome

Cytarabine syndrome sometimes happens about 6 to 12 hours after having this drug. 

It is a combination of symptoms including a high temperature, aching muscles, bone pain, occasionally chest pain, a rash, sore eyes, and extreme weakness. Steroids can help to prevent or treat this syndrome.

Biopsy and blood test results

This drug can cause abnormal results. Your doctor or nurse might need to take more biopsies or blood tests. Talk to your team about this. 

Possible additional common side effects if you have high dose cytarabine treatment

You might have additional common side effects from high dose cytarabine. Each of these effects happens in more than 10 in 100 people (more than 10%). You might have one or more of them.

Any other side effects may also be more severe. Ask your healthcare team if you are having high dose cytarabine if you are not sure.

After treatment with high doses of cytarabine it is common to have one or more side effects affecting the brain. These might include personality changes or changes involving movement or speech. We have given information about how likely each individual side effect is where possible.

Feeling very sleepy

You might feel very tired or find you are falling asleep during the day. Do not drive or operate machinery. Let your doctor know straight away. 

Fluid in the lungs (pulmonary oedema)

The fluid stops your lungs expanding fully. So, you have to take shallower breaths and make more effort to breathe. Talk to the team looking after you if you are breathless. 

Inflammation of the lungs due to infection or injury

You might have symptoms that include fast and shallow breathing, tiredness, drowsiness, confusion, feeling like you will faint and shortness of breath. This is called acute respiratory distress syndrome (ARDS). It causes lack of oxygen to your organs such as the lungs, heart and brain. 

Contact your team or advice line straight away

Difficulty with movement and speech

You might have problems with your speech. Occasionally this might be because of weakness in the muscles used for speech. You might be unsteady when you stand and find it difficult to walk. You might have no muscle control causing coordination problems.

Tiredness and weakness (fatigue)

Tiredness and weakness (fatigue) can happen during and after treatment. Doing gentle exercises each day can keep your energy up. Don't push yourself, rest when you start to feel tired and ask others for help.

Eye changes 

You might have eye problems including blurred vision, sore, red, itchy, dry eyes (conjunctivitis) or an infection. Tell your healthcare team if you have this. They can give you eye drops or other medication to help. 

Occasionally you might have jittery movements of your eyes.

You have steroid eye drops to try and prevent conjunctivitis during treatment with high dose cytarabine. Your healthcare team can explain more.

Occasional side effects

Each of these effects happens in between 1 and 10 in 100 people (between 1% and 10%). You might have one or more of them. They include:

  • skin ulcers
  • swallowing problems (dysphagia)
  • a blood clot at the injection site
  • infection at injection site
  • kidney problems – such as finding it difficult to fully empty your bladder (urinary retention)
  • burst blood vessels in the eye with an eye infection (conjunctivitis). You may have a dislike of bright lights, have a burning sensation in the eye or a watery eye
  • loss of appetite
  • high levels of uric acid in the blood

Possible additional occasional side effects if you have high dose cytarabine treatment

These side effects happen in between 1 and 10 out of every 100 people (between 1 and 10%). You might have one or more of them. They include:

  • inflammation and decreased blood supply to the bowel (colitis) – this can be very serious
  • peeling of the skin

Rare side effects

These side effects happen in fewer than 1 in 100 people (less than 1%). You might have one or more of them. They include:

  • sore throat
  • gas in the bowel wall or inflammation of the bowel wall
  • pain in the muscles or joints
  • inflammation of the heart
  • inflammation or ulceration of the food pipe (oesophagus)
  • redness, soreness and peeling of hands and soles of feet (palmar plantar syndrome)

Other side effects

There isn't enough information to work out how often these side effects might happen. You might have one or more of them. They include:

  • allergic reaction which might lead to swelling underneath the skin in areas such as the hands, feet, lips, tongue, around the eyes or gentials (angioedema)
  • lowered appetite
  • inflammation of the nerves, headaches or dizziness
  • heart problems such as changes in heart rate, build up of fluid around the heart (pericardial effusion) or chest pain
  • inflammation of the pancreas (pancreatitis)
  • yellowing of the eyes or whites of the eyes (jaundice)

Possible additional other side effects if you have high dose cytarabine treatment

There isn't enough information to work out how often these side effects might happen. You might have one or more of them. They include:

  • personality changes
  • coma
  • fits (seizures)
  • numbness, weakness or tingling in the hands and feet
  • long term disease of the heart muscle (cardiomyopathy) - this can be life threatening
  • inflammation of the sheet of the tissue that lines the abdominal cavity and covers the organs inside it (peritoneum)
  • breakdown of muscle – this can be very serious

Coping with side effects

We have more information about side effects and tips on how to cope with them.

What else do you need to know?

Other medicines, foods and drink

Cancer drugs can interact with medicines, herbal products, and some food and drinks. We are unable to list all the possible interactions that may happen. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.

Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know about any other medical conditions or allergies you may have.

Pregnancy and contraception

This treatment may harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant while you're having treatment and for at least 6 months afterwards.

Talk to your doctor or nurse about effective contraception before starting treatment. Let them know straight away if you or your partner become pregnant while having treatment. 

Loss of fertility

You may not be able to become pregnant or get someone pregnant after treatment with this drug. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.

Men might be able to store sperm before starting treatment. And women might be able to store eggs or ovarian tissue. But these services are not available in every hospital, so you would need to ask your doctor about this.    


It is not known whether this drug comes through into the breast milk. Doctors usually advise that you don’t breastfeed during this treatment.

Treatment for other conditions

If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.


Don’t have immunisations with live vaccines while you’re having treatment and for up to 12 months afterwards. The length of time depends on the treatment you are having. Ask your doctor or pharmacist how long you should avoid live vaccinations.

In the UK, live vaccines include rubella, mumps, measles, BCG, yellow fever and one of the shingles vaccines called Zostavax.

You can have:

  • other vaccines, but they might not give you as much protection as usual
  • the flu vaccine (as an injection)
  • the coronavirus (COVID-19) vaccine - talk to your doctor or pharmacist about the best time to have it in relation to your cancer treatment

Members of your household who are aged 5 years or over are also able to have the COVID-19 vaccine. This is to help lower your risk of getting COVID-19 while having cancer treatment and until your immune system Open a glossary item recovers from treatment.

Contact with others who have had immunisations - You can be in contact with other people who have had live vaccines as injections. Avoid close contact with people who have recently had live vaccines taken by mouth (oral vaccines) such as the oral typhoid vaccine. Sometimes people who have had the live shingles vaccine can get a shingles type rash. If this happens they should keep the area covered.

If your immune system is severely weakened, you should avoid contact with children who have had the flu vaccine as a nasal spray as this is a live vaccine. This is for 2 weeks following their vaccination.

Babies have the live rotavirus vaccine. The virus is in the baby’s poo for about 2 weeks and could make you ill if your immunity is low. Get someone else to change their nappies during this time if you can. If this isn't possible, wash your hands well after changing their nappy.

More information about this treatment

For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

Related links