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Mercaptopurine is used to treat acute lymphoblastic leukemia. Common side effects include loss of appetite, nausea and vomiting, diarrhea, and rash. Serious side effects may include blood disorders or liver damage. Mercaptopurine is available as a tablet or liquid that is taken by mouth.

Uses

What is mercaptopurine used for?

Mercaptopurine is commonly used to treat acute lymphoblastic leukemia (ALL), which is a type of blood cancer.

Mercaptopurine may also be used for other conditions as determined by your health care provider.

How does mercaptopurine work (mechanism of action)?

Mercaptopurine works by preventing the DNA in cancer cells from working. This stops the cancer cells from growing and multiplying, which can help slow or stop the spread of cancer.

How is mercaptopurine supplied (dosage forms)?

Brands and other names

  • Purinethol
  • Purixan

Dosage forms and strengths

  • 2,000 mg/100 mL (20 mg/mL) oral suspension
  • 50 mg oral tablets

How should I store mercaptopurine?

Mercaptopurine should be stored at room temperature, between 68 F and 77 F (20 C and 25 C). It can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when transporting it. Store in a cool, dry place. Mercaptopurine oral liquid should be kept in the original bottle with the child-resistant cap tightly closed.

Side Effects

What are the most common side effects of mercaptopurine?

The most common side effects of mercaptopurine are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Blood disorders (see below)
  • Loss of appetite
  • Nausea and vomiting
  • Diarrhea
  • General feeling of being unwell, tired, or not having your usual energy
  • Rash

There may be other side effects of mercaptopurine that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of mercaptopurine?

While less common, the most serious side effects of mercaptopurine are described below, along with what to do if they happen.

Severe Allergic Reactions. Mercaptopurine may cause allergic reactions, which can be serious. Stop taking mercaptopurine and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Blood Disorders. Mercaptopurine can cause blood disorders, such as low red blood cell levels (anemia), low platelet levels (thrombocytopenia), and low neutrophil levels (neutropenia). It is important to go to all blood test appointments to make sure mercaptopurine is safe for you. Get help right away if you have any of the following symptoms of blood disorders.

  • Fever
  • Sore throat
  • Shortness of breath
  • Pale or yellowish skin
  • Easy bruising or bleeding
  • Frequent infections
  • Unusual weakness or tiredness
  • Dizziness, lightheadedness, or feeling like you are about to pass out
  • Headache
  • Fast or abnormal heartbeat

Liver Damage. Liver damage, also called hepatotoxicity, can happen when taking mercaptopurine. Call your health care provider right away if you have any of the following symptoms of liver damage.

  • Nausea or vomiting
  • Stomach or belly pain
  • Fever
  • Weakness or unusual tiredness
  • Itching
  • Loss of appetite
  • Light-colored poop
  • Dark-colored urine (pee)
  • Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Cancer. Mercaptopurine can cause a new cancer to develop or cause a previously treated cancer to return. Tell your health care provider about any new symptoms that you may get.

Warnings & Precautions

Who should not use mercaptopurine?

Allergies to Ingredients. People who are allergic to any of the following should not take mercaptopurine.

  • Mercaptopurine
  • Purinethol
  • Purixan
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific mercaptopurine products they stock.

What should I know about mercaptopurine before using it?

Do not take mercaptopurine unless it has been prescribed to you by a health care provider. Take it as prescribed.

Do not share mercaptopurine with other people, even if they have the same condition as you. It may harm them.

Keep mercaptopurine out of the reach of children.

It is important to attend all appointments for blood tests with your health care provider. They will use these tests to monitor your body’s response to mercaptopurine and make sure it is safe for you to continue using the medicine.

Mercaptopurine tablets should be swallowed whole and should not be crushed, cut, or chewed. 

You can take mercaptopurine with or without food, but you should do it the same way each time you take a dose. Take all doses of mercaptopurine either with food or without food.

If you are taking mercaptopurine liquid, use an accurate measuring device to measure your dose. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Ask your pharmacist what measuring device to use.

Mercaptopurine liquid should be used within eight weeks of opening the bottle. Any leftover medicine should be thrown away after eight weeks. It is important that you do not throw away the medicine in the trash or flush it down the toilet or sink. Read and follow the instructions that come with the medicine. Talk to your pharmacist or other health care provider about how to safely throw away medicine that is no longer needed. 

Wash the area with water right away if mercaptopurine comes into contact with your skin, eyes, or mouth. Get medical help if you have redness, a rash, itching, or swelling after touching mercaptopurine.

Mercaptopurine can make your skin more sensitive to light from the sun, sunlamps, and tanning beds. This is called photosensitivity. Exposure to this light can cause severe sunburns, blisters, and swelling. If you need to be in sunlight, wear sunscreen, a hat, and clothing that covers your skin.

Mercaptopurine may make it hard for you to get pregnant or get your partner pregnant. If you have concerns, talk to your health care provider.

What should I tell my health care provider before using mercaptopurine?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if mercaptopurine is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have any of the following.

  • Any other prior or current cancer
  • Prior or current infection
  • An autoimmune condition, including inflammatory bowel disease (IBD)
  • Liver problems
  • Kidney problems
  • A deficiency of the enzyme thiopurine methyltransferase (TPMT) or nudix hydrolase 15 (NUDT15)

Vaccines. Talk with your health care provider about any vaccines that you may need. You should not receive certain vaccines right before or while using mercaptopurine. Tell your health care provider about any vaccines you have recently received or have scheduled.

Other Medicines and Supplements. Mercaptopurine may interact with other medicines and supplements. Before taking mercaptopurine, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. Mercaptopurine may cause harm to a fetus. Your health care provider will make sure you are not pregnant before starting mercaptopurine. If you can get pregnant, you should use effective birth control while taking mercaptopurine and for at least six months after your last dose. If you are able to get a partner pregnant, you should use effective birth control while taking mercaptopurine and for at least three months after your last dose. Tell your health care provider right away if you are pregnant, think you might be pregnant, or plan to become pregnant.

Breastfeeding. It is not known if mercaptopurine passes into breast milk. Do not breastfeed while taking mercaptopurine and for one week after your last dose. Tell your health care provider if you are breastfeeding or plan to breastfeed. 

Interactions

Does mercaptopurine interact with foods or drinks?

There are no known interactions between mercaptopurine and foods or drinks.

It is unknown if drinking alcohol will affect mercaptopurine, but heavy drinking can slow your immune response and make it harder for your body to fight cancer. 

Does mercaptopurine interact with other medicines (drug interactions)?

Mercaptopurine interacts with many other medicines. Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking mercaptopurine. Ask your pharmacist if you are not sure whether you are taking one of these medicines.

  • Allopurinol, which is a medicine used to treat high uric acid levels or gout
  • Warfarin, which is a blood thinner
  • Sulfamethoxazole/trimethoprim, which is an antibiotic used to treat certain infections
  • An aminosalicylate, such as mesalamine, olsalazine (Dipentum), or sulfasalazine (Azulfidine), which is a medicine used for certain inflammatory conditions, such as ulcerative colitis or rheumatoid arthritis
  • Methotrexate (Trexall and others), which is a medicine commonly used for rheumatoid arthritis or certain types of cancer
  • Any medicine that can cause liver problems
  • Any medicine that may cause or worsen blood disorders

This may not be a complete list of medicines that can interact with mercaptopurine. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much mercaptopurine?

If you or someone else has used too much mercaptopurine, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of mercaptopurine?

If you miss a dose, contact your health care provider to see what you should do. They will tell you when you should take your next dose. Do not take double or extra doses.