Arsenic trioxide (Trisenox, ATO)

Arsenic trioxide is a chemotherapy drug and is also called Trisenox or ATO.

It is a treatment for a type of acute myeloid leukaemia called acute promyelocytic leukaemia (APL).

How it 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 it

You have arsenic trioxide as a drip into the bloodstream. 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.

Drugs into your bloodstream

You have the treatment through a drip into your arm or hand. A nurse puts a small tube (a cannula) into one of your veins and connects the drip to it.

You might need a central line. This is a long plastic tube that gives the drugs into a large vein, either in your chest or through a vein in your arm. It stays in while you’re having treatment, which may be for a few months.

When you have it

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

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 to 60 days.

Consolidation treatment
You usually have 20 or 25 doses of arsenic trioxide depending on if you are newly diagnosed. Or if your treatment has come back (relapsed) or not gone away (refractory). You have it for 5 days a week with a 2 day break, for 4 to 5 weeks. 


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.

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

Side effects

We haven't listed all the side effects. It's very unlikely that you will have all of these side effects, but you might have some of them at the same time.

How often and how severe the side effects are can vary from person to person. They also depend on what other treatments you're having. For example, your side effects could be worse if you're also having other drugs.

When to contact your team

Your doctor, nurse or pharmacist will go through the possible side effects. They will monitor you closely 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 doctor or nurse immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

Common side effects

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

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.

Swelling of hands and feet (oedema)

You may have swelling of your hands and legs due to a build up of fluid (oedema). 

High temperature (fever)

If you get a high temperature, let your healthcare team know straight away. Ask them if you can take paracetamol to help lower your temperature.

Skin changes

Skin problems include a skin rash, dry skin and itching. This usually goes back to normal when your treatment finishes. Your nurse will tell you what products you can use on your skin to help.

High sugar levels in the blood

You have regular blood and urine tests to check this. If you have diabetes you may need to check your blood sugar levels more often than usual. 

Numbness and tingling in fingers and toes

Numbness or tingling in fingers or toes is often temporary and can improve after you finish treatment. Tell your healthcare team if you're finding it difficult to walk or complete fiddly tasks such as doing up buttons. 


Contact your advice line if you have diarrhoea, such as if you've had 4 or more loose watery poos (stools) in 24 hours. Or if you can't drink to replace the lost fluid. Or if it carries on for more than 3 days.

Your doctor may give you anti diarrhoea medicine to take home with you after treatment. Eat less fibre, avoid raw fruits, fruit juice, cereals and vegetables, and drink plenty to replace the fluid lost.

Feeling or being sick

Feeling or being sick is usually well controlled with anti sickness medicines. Avoiding fatty or fried foods, eating small meals and snacks, drinking plenty of water, and relaxation techniques can all 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 treating it once it has started.

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.

Less commonly your blood might show high levels of bilirubin in the blood.

You have regular blood tests to check for any changes in the levels of chemicals produced by the liver.

Headaches and dizziness

Let your doctor or nurse know if you have headaches. They can give you painkillers. Don’t drive or operate machinery if you feel dizzy.

Shortness of breath 

This drug can cause lung problems. Let your doctor or nurse know straight away if you suddenly become breathless.

Heart problems 

This might be a fast heart rate (tachycardia). You will have regular heart checks during and after the treatment. Tell your doctor or nurse straight away if you have any chest pain.

Changes in mineral levels in the blood

Your blood contains different minerals and electrolytes. This treatment can change the levels of magnesium and potassium in your blood. Less commonly you might have low levels of sodium in your blood.You will have regular blood tests to check for this. 

Body pain

You might develop pain in your body. Let your team know so they can give you painkillers to help.

Fast release of immune substances into your blood

Let your team know straight away if you develop symptoms such as difficulty in breathing, a cough, chest pain or high temperature.

This could be a sign that you have differentiation syndrome. This is when you have a fast release of immune substances (cytokines) into your blood. It needs to be treated quickly as it can be life threatening. 

Occasional side effects

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

  • increased risk of getting an infection
  • breathlessness and looking pale due to a low number of red blood cells carry oxygen around your blood
  • bruising, bleeding gums or nosebleeds due to a low number of platelets in your blood
  • fluid around the heart or lungs
  • weight gain
  • kidney changes - you will have regular blood tests to check this
  • eye changes such as blurred vision
  • low blood pressure
  • seizures
  • herpes virus
  • chills
  • tummy (abdominal) pain
  • bone and joint pain
  • high number of white blood cells in your blood (leucocytosis)
  • a build up of a substance called ketones in the blood and urine (ketoacidosis)
  • inflammation of the blood vessels
  • chest pain
  • bleeding in the lung
  • reddening of the skin
  • swollen face (oedema)
  • sudden sharp, stabbing or burning pain in the chest when you take a breath in or breathe out

Other side effects

There isn't enough information to work out how often this side effect might happen. There have been a few reports of people developing a second cancer some years after arsenic trioxide treatment. It is not clear whether this was due to the arsenic or not.

Coping with side effects

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

What else do I need to know?

Other medicines, foods and drink 

Cancer drugs can interact with some other medicines and herbal products. Tell your doctor or pharmacist about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies.

Pregnancy and contraception

This treatment might harm a baby developing in the womb. It is important not to become pregnant or father a child while you're having treatment and for a few months afterwards.

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


It is not known whether this treatment affects fertility in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.


Don’t breastfeed during this treatment because the drug may come through into your breast milk.

Treatment for other conditions

Always tell other doctors, nurses, pharmacists or dentists that you’re having this treatment if you need treatment for anything else, including teeth problems.


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 go to the electronic Medicines Compendium (eMC) website.

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

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