Mercaptopurine Tablets

  • Puri-Nethol contains mercaptopurine monohydrate as the active ingredient. It belongs to a group of medicines called cytotoxics.
  • Puri-Nethol is used solely or in combination with other medicines to treat acute leukaemia, a cancer of certain blood cells.
  • It works by interfering with the growth of cancer cells.

Pharmacist - M.B.A. (Public Health) D.I.C.

Mercaptopurine Tablets

What is it used for? Acute leukaemia, in…

Garvan J. Lynch
MBA (Public Health)

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What is it used for?

  • Acute leukaemia, in particular maintenance treatment for acute lymphoblastic leukaemia and acute myelogenous leukaemia.
  • Chronic myeloid leukaemia (CML).
  • Inflammatory bowel disease such as ulcerative colitis or Crohn's disease (unlicensed use).

How does it work?

  • Puri-Nethol tablets contain the active ingredient mercaptopurine, which is a type of chemotherapy medicine for cancer known as a 'cytotoxic antimetabolite'. It is used to treat various types of leukaemia.
  • The bone marrow produces cells called stem cells. These normally develop into the different types of blood cells (white blood cells, red blood cells and platelets) and when these are mature they leave the bone marrow and enter the bloodstream. In leukaemia the bone marrow produces too many immature white blood cells. These abnormal cells take up space in the bone marrow and result in less room for production of normal healthy blood cells.
  • Mercaptopurine works by stopping the abnormal blood cells from multiplying. It does this by being incorporated into the cells' genetic material, DNA and RNA. Both DNA and RNA are needed for cells to grow, repair themselves and multiply. Mercaptopurine causes problems with the production of DNA and RNA in the cancer cells, and this causes the cells to grow in an unbalanced way, resulting in the death of the cells.
  • Unfortunately, mercaptopurine can also affect normal, healthy cells, particularly those that multiply quickly, such as blood cells and hair cells. Although the aim of treating leukaemia with mercaptopurine is to kill the cancerous blood cells, the most important side effect is on the bone marrow, where blood cells are made. Mercaptopurine also decreases the production of normal blood cells, which can leave people susceptible to infection. Regular blood tests are therefore needed to monitor the levels of blood cells.
  • In most chemotherapy regimens, doses are administered in courses at various intervals to allow normal cells to recover from the adverse effects of the anticancer medicines between doses. However, during this period, cancer cells will also recover and start to replicate again. Successful treatment depends on the administration of the next course of therapy before the cancer cells reach their previous numbers and the net effect is to decrease the amount of cancer with each successive course.

How do I take it?

  • It is important to follow the instructions that your doctor has given you for taking this medicine. The number of tablets to take and how often will vary from person to person and may change each week depending on the results of your blood tests. It is important to follow the instructions given by your doctor and printed on the dispensing label. Ask your doctor or pharmacist for advice if you are unsure about anything.
  • Puri-Nethol tablets can be taken either with or without food. The tablets should be swallowed whole with a drink of water.
  • If you need to break a tablet in half, make sure you don't breathe in any powder that is produced when you break it. Wash your hands after breaking a tablet.
  • Women who are pregnant should not handle these tablets.
  • If you forget to take a dose you should tell your doctor. Do not take a double dose to make up for a missed dose.
  • Make sure these tablets are kept out of the sight and reach of children.


  • This medicine (as well as leukaemia itself) can decrease the number of healthy blood cells in your blood. A low white blood cell count can increase your susceptibility to infections, a low red blood cell count causes anaemia and a low platelet count can cause problems with blood clotting. For this reason, you will need regular blood tests to monitor your blood cells during treatment with this medicine. Tell your doctor immediately if you experience any of the following symptoms during your treatment, as they may indicate problems with your blood cells: unexplained bruising or bleeding, purple spots, sore mouth or throat, mouth ulcers, high temperature (fever) or other signs of infection, or suddenly feeling tired, breathless, or generally unwell.
  • People having treatment with this medicine will also need regular blood tests to monitor their liver function. Symptoms that may suggest a liver problem include persistent nausea and vomiting, abdominal pain, or the development of jaundice (a yellow colouring to the skin and the whites of the eyes). Tell your doctor if you or your child experiences any of these symptoms.
  • During treatment to induce remission of leukaemia, this medicine causes rapid cell breakdown. The products of the cell breakdown, in particular uric acid, can build up in the blood or urine and can cause kidney problems. For this reason, people having remission induction treatment will need to have regular blood and urine tests to monitor their uric acid levels. If these go too high your doctor may prescribe another medicine called allopurinol to reduce them.
  • This medicine may be harmful to an unborn baby, and for this reason you should use an effective method of contraception to avoid getting pregnant or fathering a child during treatment. You should continue to use contraception to prevent pregnancy for at least a few months after treatment with this medicine is stopped. Women should consult their doctor immediately if they get pregnant during treatment.
  • Your ability to become pregnant or father a child may be affected by this medicine. It is important to discuss fertility with your doctor before starting treatment.

Use with caution in

  • Decreased kidney function.
  • Decreased liver function or liver disease.
  • People with a inherited condition where the body does not produce enough of an enzyme called TMPT (thiopurine methyltransferase deficiency).

Not to be used in

  • Breastfeeding.
  • This medicine should not be used if you are allergic to any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.

If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and breastfeeding

  • This medicine should not be used in pregnancy, unless considered essential by your doctor due to life-threatening disease, because it may be harmful to a developing baby. In addition, pregnant women should not handle this medicine.
  • Women who could get pregnant should use effective contraception to prevent pregnancy, and men should use effective contraception to prevent fathering a child, both during treatment, and for at least a few months after treatment is finished. Seek medical advice from your doctor.
  • This medicine may pass into breast milk and may be harmful to a nursing infant. Mothers who need treatment with this medicine should not breastfeed. Seek medical advice from your doctor.

Side effects

  • Decrease in the number of white blood cells in the blood (leucopenia). 
  • Decrease in the number of platelets in the blood (thrombocytopenia).
  • Feeling or being sick. You will be given medicines to help prevent this.
  • Blockage of bile flow.
  • Liver problems.
  • Inflammation of the pancreas (pancreatitis) in people being treated for inflammatory bowel diseases. Pancreatitis occurs rarely in people being treated for leukaemia.
  • Decrease in the number of red blood cells in the blood (anaemia).
  • Loss of appetite.
  • Pain in the joints.
  • Skin rash.
  • Fever.
  • Mouth ulcers.
  • Hair loss.
  • Temporary decrease in sperm count.
  • Ulcers in the intestines.
  • Swelling of the face.

Leukaemia. After your treatment you will have regular blood tests which will detect any possible leukaemic changes early, if they do occur. Your doctor or nurse can discuss the risks of this with you.
The side effects listed above may not include all of the side effects reported by the medicine's manufacturer.

For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

  • It is important to tell your doctor or pharmacist what medicines you or your child are already taking, including those bought without a prescription and herbal medicines, before treatment with this medicine is started. Similarly, check with your doctor or pharmacist before taking any new medicines during treatment this one, to make sure that the combination is safe.
  • Vaccines may be less effective in people receiving chemotherapy. This is because chemotherapy medicines reduce the activity of the immune system and can prevent the body forming adequate antibodies. Live vaccines should be postponed until at least six months after finishing chemotherapy because they may cause infection. Live vaccines include the following: oral polio; rubella; measles, mumps and rubella (MMR); BCG; chickenpox; yellow fever and oral typhoid vaccines.
  • Allopurinol increases the blood level of mercaptopurine, which may increase the risk of side effects. For this reason, if you are given allopurinol during treatment to lower the amount of uric acid in your blood, your doctor will lower your dose of mercaptopurine.
  • Aminosalicylate medicines (eg olsalazine, mesalazine or sulfazalazine) may also interfere with the breakdown of mercaptopurine and increase its blood level. This may increase the risk of a drop in healthy white blood cell count. These medicines should be used with caution in combination with mercaptopurine.
  • Mercaptopurine may decrease the anti-blood-clotting effect of the anticoagulant medicine warfarin. People taking warfarin should have their blood clotting time monitored during treatment with this medicine. The dose of the anticoagulant may need increasing.
  • There may be an increased risk of side effects on the liver or blood cells if this medicine is used in combination with other treatments that can affect the liver or blood cells, for example other chemotherapy medicines, or the antipsychotic clozapine.


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