Brand Name(s):

  • Purinethol®

Other Name(s):

  • 6-MP

WHY is this medicine prescribed?

Mercaptopurine is used to treat acute lymphocytic leukemia (ALL; also called acute lymphoblastic leukemia and acute lymphatic leukemia; a type of cancer that begins in the white blood cells). Mercaptopurine is in a class of medications called purine antagonists. It works by stopping the growth of cancer cells.

HOW should this medicine be used?

Mercaptopurine comes as a tablet to take by mouth. It is usually taken once a day. Take mercaptopurine at around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take mercaptopurine exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Continue to take mercaptopurine even if you feel well. Do not stop taking mercaptopurine without talking to your doctor

Are there OTHER USES for this medicine?

Mercaptopurine is also sometimes used to treat certain other types of cancer, Crohn's disease (a condition in which the body attacks the lining of the digestive tract causing pain, diarrhea, weight loss, and fever), and ulcerative colitis (a condition which causes swelling and sores in the lining of the colon [large intestine] and rectum). Talk to your doctor about the possible risks of using this medication for your condition.

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

What SPECIAL PRECAUTIONS should I follow?

Before taking mercaptopurine,

  • tell your doctor and pharmacist if you are allergic to mercaptopurine, any other medications, or any of the ingredients in mercaptopurine tablets. Ask your pharmacist for a list of the ingredients.
  • tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: allopurinol (Zyloprim); aminosalicylates such as mesalamine (Apriso, Asacol, Pentasa, others), olsalazine (Dipentum), and sulfasalazine (Azulfidine); anticoagulants ('blood thinners') such as warfarin (Coumadin); doxorubicin (Doxil); and trimethoprim and sulfamethoxazole (Bactrim, Septra). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
  • tell your doctor if you have already taken mercaptopurine or thioguanine to treat your cancer. Your doctor may tell you not to take mercaptopurine if either of these medications did not work well against your cancer in the past.
  • tell your doctor if you have any type of infection and if you have or have ever had liver or kidney disease.
  • tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. You should use birth control to avoid pregnancy during your treatment with mercaptopurine. If you become pregnant while taking mercaptopurine, call your doctor. Mercaptopurine may harm the fetus.
  • if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking mercaptopurine.
  • do not have any vaccinations without talking to your doctor.
  • you should know that the risk that you will develop serious side effects of mercaptopurine may be higher if you have a genetic (inherited) risk factor. Your doctor may order tests before or during your treatment to see if you have this risk factor.

What SPECIAL DIETARY instructions should I follow?

Unless your doctor tells you otherwise, continue your normal diet.

Drink plenty of fluids during your treatment with mercaptopurine.

What should I do IF I FORGET to take a dose?

Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

What SIDE EFFECTS can this medicine cause?

Mercaptopurine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • nausea
  • vomiting
  • darkening of the skin
  • hair loss
  • rash

Some side effects can be serious. If you experience any of these symptoms, call your doctor immediately:

  • pale skin
  • weakness
  • shortness of breath
  • sore throat, fever, chills, or other signs of infection
  • unusual bruising or bleeding
  • yellowing of the skin or eyes
  • loss of appetite
  • diarrhea
  • swelling of the stomach area
  • pain in the upper right part of the stomach

Taking mercaptopurine may increase the risk that you will develop a new cancer. Some people who took mercaptopurine to treat Crohn's disease or ulcerative colitis developed hepatosplenic T cell lymphoma (HSTCL), a very serious form of cancer that often causes death within a short time. Tell your doctor if you experience any of the following symptoms: stomach pain; fever; unexplained weight loss; night sweats or easy bruising or bleeding. Talk to your doctor about the risks of taking this medication.

Mercaptopurine may cause other side effects. Call your doctor if you have any unusual problems while you are taking this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online [at Web Site] or by phone [1-800-332-1088].

What should I know about STORAGE and DISPOSAL of this medication?

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom). Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.

What should I do in case of OVERDOSE?

In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911.

Symptoms of overdose may include:

  • loss of appetite
  • nausea
  • vomiting
  • diarrhea
  • pale skin
  • weakness
  • shortness of breath
  • sore throat, fever, chills, and other signs of infection
  • unusual bruising or bleeding

What OTHER INFORMATION should I know?

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your body's response to mercaptopurine.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.

AHFS® Consumer Medication Information. © Copyright, The American Society of Health-System Pharmacists, Inc., 7272 Wisconsin Avenue, Bethesda, Maryland. All Rights Reserved. Duplication for commercial use must be authorized by ASHP.

Selected Revisions: May 15, 2014.