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Mercaptopurine (Purinethol)

Article Translations: (Spanish)

How does this medicine work?

Mercaptopurine (mer-cap-toe-pure-een, also called 6-MP) destroys cancer cells by interfering with a specific phase of the cells' life cycle.

How is it given?

6-MP is given by mouth. Give it at regular times to keep a steady level in the bloodstream. Your child should be awake and alert when taking any medicine.

___ For children who cannot swallow tablets:

  1. Put on gloves.
  2. Crush the tablet in a tablet crusher or between 2 spoons inside a clear plastic bag.
  3. Mix the powder with a very small amount (about 1 teaspoon) of clear jelly or flavored syrup such as chocolate or cherry. Do not mix it with milk products. Make sure your child takes all of the mixture.
  4. Wash spoons and container right after use. Discard the plastic bag and gloves.

Are there any precautions about food or other medicines?

Mercaptopurine can be taken any time of day with or without food.

Avoid alcohol-containing beverages while on this medicine. Check with the doctor, nurse practitioner, or pharmacist before giving any other prescription or non-prescription medicines, herbs or vitamins.

What should I do if a dose is missed?

If one dose is missed, you should make it up the next day. This will not cause side-effects because it works slowly over time.

If your child throws up within 30 minutes after receiving a dose, give it again. If your child vomits after 30 minutes, do not repeat the dose. Call the oncology clinic if more than one dose is missed or vomited.

What are the side effects?


  • low blood cell counts


  • loss of appetite
  • mild nausea (if this occurs in the morning it could be a sign of low blood sugar from 6-MP) 
  • vomiting (if this occurs in the morning it could be a sign of low blood sugar from 6-MP)
  • skin rash
  • changes in liver a liver test (ALT) which does not result in liver damage


  • diarrhea
  • lung changes
  • increased sun sensitivity

When should I call the doctor?

  • morning nausea or vomiting
  • fever
  • sore throat
  • bleeding
  • unusual bruising
  • shortness of breath
  • pain when urinating
  • signs of allergic reaction:
    • rash or hives
    • wheezing
    • trouble breathing - call 911

What else do I need to know?

All caregivers should wear gloves when handling urine, stool, and vomit while your child is receiving the chemotherapy and for 48 hours afterward. Urine, stool, and vomit can be safely disposed of in septic tanks and the sewer system.

Any clothing or bed linens that are contaminated with urine, stool, or vomit should be washed separately from other laundry in hot water and detergent. Anyone handling the contaminated laundry should wear gloves.

Blood tests will be done at times and the dose of 6-MP will be adjusted to keep the absolute neutrophil count above 1,000.

You and your child should know the names of all the medicines he or she is taking. Share this information with anyone involved in your child's care.

Always make sure you have enough medicine on hand. Each time you refill your prescriptions, check to see how many refills are left. If no refills are left, the pharmacist will need 2 or 3 days to contact the doctor to renew the prescription.

Before giving the first dose, read the label. Be sure it is what was prescribed. After a refill, if the medicine looks different to you, ask your pharmacist or call the oncology clinic before giving it.

Check the label for the expiration date. Bring outdated or extra medicines back to the clinic or pharmacy for disposal. Do not flush them down the toilet or throw them in the garbage.

Store all medicines in their original container and away from direct sunlight or heat. Do not store in humid places such as the bathroom. Keep them out of children's reach, locked up if possible.

If too much or the wrong kind of chemotherapy medicine is taken, call the oncology clinic right away. If your child is unconscious or has a seizure, call 911.


This information is not specific to your child but provides general information. If you have any questions, please call the oncology clinic or pharmacy.

Reviewed 6/2016 

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This page is not specific to your child, but provides general information on the topic above. If you have any questions, please call your clinic. For more reading material about this and other health topics, please call or visit Children's Minnesota Family Resource Center library, or visit

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