Tioguanine (thioguanine, 6-TG, 6-tioguanine) | Cancer Research UK
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Tioguanine (thioguanine, 6-TG, 6-tioguanine)

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This page tells you about the chemotherapy drug tioguanine (thioguanine) and its possible side effects. There is information about


What tioguanine is

Tioguanine used to be called thioguanine. It is a chemotherapy drug used for 

  • Acute myeloid leukaemia
  • Acute lymphoblastic leukaemia
  • Chronic myeloid leukaemia

How tioguanine works

It is one of a group of chemotherapy drugs known as anti metabolites. These drugs stop cells making and repairing DNA. Cancer cells need to make and repair DNA so that they can grow and multiply.


How you have tioguanine

Tioguanine comes as 40mg white, or off white, tablets. Take them on an empty stomach with plenty of water (for example, at least 1 hour before or 2 hours after meals). If you need to break your tablet in half, wash your hands straight afterwards. Be careful not to breathe in any powder that the tablet releases.

It is very important that you take 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. You should take the right dose, not more or less. And never stop taking a cancer drug without talking to your specialist first.

If you accidentally take more tioguanine than you should, tell your doctor straight away or go to a hospital. Take the medicine pack with you. 

If you forget to take tioguanine, tell your doctor. Don't take a double dose to make up for the missed dose.

You usually have chemotherapy as a course of several cycles of treatment. The treatment plan for tioguanine depends on which type of cancer you have. 


Tests during treatment

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


About side effects

We've listed the side effects associated with tioguanine. 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 tioguanine 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.

  • 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
  • Tiredness and breathlessness 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)
  • Tiredness and weakness (fatigue) during and after treatment – most people find their energy levels are back to normal from 6 months to a year after their treatment ends
  • Liver changes that usually go back to normal when you stop treatment – this is not likely to harm you

Occasional side effects

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

  • Diarrhoea is usually well controlled with medicine from your doctor or nurse – drink plenty of fluids if you get diarrhoea
  • Loss of appetite
  • A sore mouth and mouth ulcers
  • Feeling or being sick is most likely to start within 24 hours. It is usually easily controlled with anti sickness injections and tablets. Tell your doctor or nurse if you still have sickness as there will be other medicines you can try
  • High uric acid levels in your blood (tumour lysis syndrome) – you may have a tablet called allopurinol to take. Drinking plenty of fluids helps to flush out the excess uric acid
  • Liver damage – this can cause yellowing of the eyes and skin. You may also have dark urine or swelling of the liver. Tell your doctor or nurse straight away if you notice swelling or discomfort on the right side under your lower ribs

Rare side effects

Fewer than 1 in 100 people have these.

  • Unsteadiness when walking
  • A skin rash
  • Women may stop having periods (amenorrhoea) but this may only be temporary
  • 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

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.

Other conditions

It is possible that tioguanine may not work for people who have Lesche-Nyhan syndrome. This syndrome is an inherited disorder in which people have very low levels of a protein called needed to make tioguanine work. 

Tioguanine may cause very severe side effects if you have a condition where your body produces too little of something called TPMT (thiopurine methyltransferase). Your doctor may do blood tests to check the levels before you start treatment. 


Immunisations and chemotherapy

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

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 www.medicines.org.uk.

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 yellowcard.mhra.gov.uk.

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Updated: 22 December 2015