Arsenic trioxide (Trisenox, ATO) | Cancer Research UK
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What arsenic trioxide is

Arsenic trioxide is a chemotherapy drug treatment for a type of acute myeloid leukaemia called acute promyelocytic leukaemia (APL). It is also called Trisenox or ATO.

Research is looking into it as a treatment for other types of cancer.


How arsenic trioxide works

Arsenic works by speeding up the death of leukaemic cells and encouraging normal blood cells to develop properly. It does this by working on particular proteins within the cell.


How you have arsenic trioxide

Arsenic trioxide is a colourless fluid. You have it into your bloodstream. You can have it through a thin, short tube (a cannula) put into a vein in your arm each time you have treatment. Or you may have it through a central line, a portacath, or a PICC line. These are long, plastic tubes that give the drugs directly into a large vein in your chest. You have the tube put in before or during your course of treatment and it stays in place as long as you need it.

The drip lasts for between 1 and 2 hours. But if you have a reaction to the drip you may have it more slowly over 4 hours. 

You can read our information about having cancer drugs.

You may have arsenic trioxide to get rid of the leukaemic cells (induction treatment) or to stop your leukaemia coming back (consolidation treatment).

For induction treatment you have arsenic trioxide every day until there is no sign of the leukaemia in your bone marrow. This is called remission induction. You have this induction treatment for up to 50 days.

For consolidation treatment you usually have 25 doses of arsenic trioxide. You generally have it for 5 days a week with a 2 day break, for 5 weeks.


Tests during treatment

You have blood tests before starting treatment and regularly during your treatment. The tests check your levels of blood cells and of certain chemicals in your blood. You may also have blood tests to check how well your liver and kidneys are working.

Before treatment and regularly during the treatment you have a test of your heart called an ECG.


About side effects

We've listed the side effects associated with arsenic trioxide. You can use the links to find out more about each side effect. Where there is no link, please go to our information about cancer drug side effects or use the search box at the top of the page.

You may have a few side effects. They 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)

The side effects may be different if you are having arsenic trioxide with other medicines.

Tell your doctor, nurse or pharmacist straight away if any of the side effects get severe.


Common side effects

More than 10 in every 100 people have one or more of the side effects listed below.

  • Tiredness and weakness (fatigue) occurs in up to 6 out of 10 people (60%) during and after treatment. Most people find their energy levels are back to normal within 6 months to a year
  • Stomach pain happens in 6 out of 10 people (60%)
  • Muscle and bone pain
  • A high temperature (fever)
  • Headaches
  • Feeling or being sick – this is usually well controlled with anti sickness medicines
  • Diarrhoea – drink plenty of fluids. Tell your doctor or nurse if diarrhoea becomes severe or continues for more than 3 days
  • Numbness or tingling in fingers and toes, which can cause difficulty with fiddly things such as doing up buttons
  • Dizziness
  • Skin changes – including a rash, dryness, itching or darkening of the skin
  • Swelling of your legs, due to fluid build up known as peripheral oedema
  • Raised blood sugar levels – you will have regular blood and urine tests to check this. Let your doctor or nurse know if you feel thirsty or need to pass urine a lot
  • Retinoic acid syndrome occurs in 1 out of 4 people (25%) – this causes shortness of breath, a high temperature (fever), chest pain, and fluid on the lung and heart. It most commonly happens 2 to 3 weeks after starting treatment and can become very serious. Tell your doctor or nurse straight away if you become breathless
  • Loss of fertility – you may not be able to become pregnant or father a child 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 may be able to store sperm before starting treatment
  • Liver changes that are very mild and unlikely to cause symptoms – they usually go back to normal when treatment is finished

Occasional side effects

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

  • 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
  • Breathlessness and looking pale due to a drop in red blood cells (anaemia) – you may need a blood transfusion
  • Bruising more easily due to a drop in platelets – 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)
  • Heart problems – sometimes arsenic can affect the way your heart works, causing low blood pressure, dizziness, chest pain, or changes in heart rhythm (heart beat). These nearly always get better when treatment has stopped. Tell your doctor if you have had heart problems before or if you have any of these effects
  • Loss of appetite
  • Inflammation around the drip site – if you notice any signs of redness, swelling or leaking at your drip site, tell your nurse straight away
  • Difficulty sleeping
  • Chills
  • Sadness and anxiety
  • Inflammation of the membrane around the lungs – let your doctor or nurse know if you have pain in your chest when you breathe
  • Weight gain
  • Kidney changes that are mild and unlikely to cause symptoms – they will usually go back to normal when treatment ends
  • Confusion
  • Dry eyes and blurred vision - your nurse can give you eyedrops to help
  • Low blood pressure
  • Earache and ringing in your ears
  • A cough and general shortness of breath
  • Nosebleeds
  • Fits (seizures)
  • Shingles sores

Rare side effects

There have been a few reports of people developing a second cancer after arsenic trioxide treatment treatment. It is not clear yet whether this was due to the arsenic or not.


Important points to remember

Talk to your doctor, pharmacist or nurse about all your side effects so 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

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

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.


Don't breastfeed during this treatment because the drug may come through in the breast milk.


Immunisations and chemotherapy

You shouldn't have immunisations with live vaccines while you are having 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.


Related information


More information about arsenic trioxide

This page doesn'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 not mentioned here that you think may be due to this treatment you can report it to the Medicines Health and Regulatory Authority (MHRA) at

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Updated: 28 January 2016