In the U.S.—

In Canada—

Another commonly used name is 6-MP.

• Antineoplastic
• Immunosuppressant

Mercaptopurine (mer-kap-toe-PYOOR-een ) belongs to the group of medicines known as antimetabolites. It is used to treat some kinds of cancer.

Mercaptopurine interferes with the growth of cancer cells, which are eventually destroyed. Since the growth of normal body cells may also be affected by mercaptopurine, other effects will also occur. Some of these may be serious and must be reported to your doctor. Other effects may not be serious but may cause concern. Some effects may not occur for months or years after the medicine is used.

Before you begin treatment with mercaptopurine, you and your doctor should talk about the good this medicine will do as well as the risks of using it.

Mercaptopurine may also be used for other conditions as determined by your doctor.

Mercaptopurine is available only with your doctor's prescription, in the following dosage form:

Oral
• Tablets (U.S. and Canada)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For mercaptopurine, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to mercaptopurine.

Pregnancy—Tell your doctor if you are pregnant or if you intend to have children. There is a chance that this medicine may cause birth defects if either the male or female is taking it at the time of conception or if it is taken during pregnancy. However, studies have not been done in humans. Mercaptopurine has been shown to cause damage to the fetus in rats and increases the risk of miscarriage or premature births in humans. In addition, many cancer medicines may cause sterility which could be permanent. Although this has not been reported with this medicine, the possibility should be kept in mind.

Be sure that you have discussed this with your doctor before taking this medicine. It is best to use some kind of birth control while you are taking mercaptopurine. Tell your doctor right away if you think you have become pregnant while taking mercaptopurine.

Breast-feeding—Tell your doctor if you are breast-feeding or if you intend to breast-feed during treatment with this medicine. Because mercaptopurine may cause serious side effects, breast-feeding is generally not recommended while you are taking it.

Children—Although there is no specific information comparing use of mercaptopurine in children with use in other age groups, it is not expected to cause different side effects or problems in children than it does in adults.

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults or if they cause different side effects or problems in older people. There is no specific information comparing use of mercaptopurine in the elderly with use in other age groups.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking mercaptopurine, it is especially important that your health care professional know if you are taking any of the following:

• Acetaminophen (e.g., Tylenol) (with long-term, high-dose use) or
• Amiodarone (e.g., Cordarone) or
• Anabolic steroids (nandrolone [e.g., Anabolin], oxandrolone [e.g., Anavar], oxymetholone [e.g., Anadrol], stanozolol [e.g., Winstrol]) or
• Androgens (male hormones) or
• Anti-infectives by mouth or by injection (medicine for infection) or
• Antithyroid agents (medicine for overactive thyroid) or
• Carbamazepine (e.g., Tegretol) or
• Chloroquine (e.g., Aralen) or
• Dantrolene (e.g., Dantrium) or
• Disulfiram (e.g., Antabuse) or
• Divalproex (e.g., Depakote) or
• Estrogens (female hormones) or
• Etretinate (e.g., Tegison) or
• Gold salts (medicine for arthritis) or
• Hydroxychloroquine (e.g., Plaquenil) or
• Methyldopa (e.g., Aldomet) or
• Naltrexone (e.g., Trexan) (with long-term, high-dose use) or
• Oral contraceptives (birth control pills) containing estrogen or
• Phenothiazines (acetophenazine [e.g., Tindal], chlorpromazine [e.g., Thorazine], fluphenazine [e.g., Prolixin], mesoridazine [e.g., Serentil], perphenazine [e.g., Trilafon], prochlorperazine [e.g., Compazine], promazine [e.g., Sparine], promethazine [e.g., Phenergan], thioridazine [e.g., Mellaril], trifluoperazine [e.g., Stelazine], triflupromazine [e.g., Vesprin], trimeprazine [e.g., Temaril]) or
• Phenytoin (e.g., Dilantin) or
• Plicamycin (e.g., Mithracin) or
• Valproic acid (e.g., Depakene)—Risk of unwanted effects on the liver may be increased

• Azathioprine (e.g., Imuran) or
• Corticosteroids (cortisone-like medicine) or
• Cyclosporine (e.g., Sandimmune) or
• Muromonab-CD3 (monoclonal antibody) (e.g., Orthoclone OKT3)—There may be an increased risk of infection and development of cancer because mercaptopurine reduces the body's immunity

• Allopurinol (e.g., Zyloprim)—Effects of mercaptopurine may be increased because allopurinol blocks its removal from the body

• Amphotericin B by injection (e.g., Fungizone) or
• Antithyroid agents (medicine for overactive thyroid) or
• Azathioprine (e.g., Imuran) or
• Chloramphenicol (e.g., Chloromycetin) or
• Colchicine or
• Flucytosine (e.g., Ancobon) or
• Ganciclovir (e.g., Cytovene) or
• Interferon (e.g., Intron A, Roferon-A) or
• Plicamycin (e.g., Mithracin) or
• Zidovudine (e.g., AZT, Retrovir) or
• If you have ever been treated with radiation or cancer medicines—Mercaptopurine may increase the effects of these medicines or radiation therapy on the blood

• Probenecid (e.g., Benemid) or
• Sulfinpyrazone (e.g., Anturane)—Mercaptopurine may raise the concentration of uric acid in the blood. Since these medicines are used to lower uric acid levels, they may not be as effective in patients taking mercaptopurine

• Chickenpox (including recent exposure) or
• Herpes zoster (shingles)—Risk of severe disease affecting other parts of the body

• Gout (history of) or
• Kidney stones (history of)—Mercaptopurine may increase levels of uric acid in the body, which can cause gout or kidney stones

• Infection—Mercaptopurine may decrease your body's ability to fight infection

• Kidney disease or
• Liver disease—Effects of mercaptopurine may be increased because of slower removal from the body

Use this medicine only as directed by your doctor. Do not use more or less of it, and do not use it more often than your doctor ordered. The exact amount of medicine you need has been carefully worked out. Taking too much may increase the chance of side effects, while taking too little may not improve your condition.

Mercaptopurine is often given together with certain other medicines. If you are using a combination of medicines, make sure that you take each one at the right time and do not mix them. Ask your health care professional to help you plan a way to remember to take your medicines at the right times.

While you are using mercaptopurine, your doctor may want you to drink extra fluids so that you will pass more urine. This will help prevent kidney problems and keep your kidneys working well.

If you vomit shortly after taking a dose of mercaptopurine, check with your doctor. You will be told whether to take the dose again or to wait until the next scheduled dose.

Dosing—

The dose of mercaptopurine will be different for different patients. The dose that is used may depend on a number of things, including what the medicine is being used for, the patient's weight, and whether or not other medicines are also being taken. If you are taking mercaptopurine at home, follow your doctor's orders or the directions on the label. If you have any questions about the proper dose of mercaptopurine, ask your doctor.

Missed dose—

If you miss a dose of this medicine, do not take the missed dose at all and do not double the next one. Instead, go back to your regular dosing schedule and check with your doctor.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

It is very important that your doctor check your progress at regular visits to make sure that this medicine is working properly and to check for unwanted effects.

Avoid alcoholic beverages until you have discussed their use with your doctor. Alcohol may increase the harmful effects of this medicine.

While you are being treated with mercaptopurine, and after you stop treatment with it, do not have any immunizations (vaccinations) without your doctor's approval. Mercaptopurine may lower your body's resistance and there is a chance you might get the infection the immunization is meant to prevent. In addition, other persons living in your household should not take oral polio vaccine since there is a chance they could pass the polio virus on to you. Also, avoid persons who have taken oral polio vaccine. Do not get close to them and do not stay in the same room with them for very long. If you cannot take these precautions, you should consider wearing a protective face mask that covers the nose and mouth.

Mercaptopurine can temporarily lower the number of white blood cells in your blood, increasing the chance of getting an infection. It can also lower the number of platelets, which are necessary for proper blood clotting. If this occurs, there are certain precautions you can take, especially when your blood count is low, to reduce the risk of infection or bleeding:

• If you can, avoid people with infections. Check with your doctor immediately if you think you are getting an infection or if you get a fever or chills, cough or hoarseness, lower back or side pain, or painful or difficult urination.
• Check with your doctor immediately if you notice any unusual bleeding or bruising; black, tarry stools; blood in urine or stools; or pinpoint red spots on your skin.
• Be careful when using a regular toothbrush, dental floss, or toothpick. Your medical doctor, dentist, or nurse may recommend other ways to clean your teeth and gums. Check with your medical doctor before having any dental work done.
• Do not touch your eyes or the inside of your nose unless you have just washed your hands and have not touched anything else in the meantime.
• Be careful not to cut yourself when you are using sharp objects such as a safety razor or fingernail or toenail cutters.
• Avoid contact sports or other situations where bruising or injury could occur.

Tell the doctor in charge that you are taking this medicine before you have any medical tests. The results of tests for the amount of sugar or uric acid in the blood measured by a machine called a sequential multiple analyzer (SMA) may be affected by this medicine.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Also, because of the way cancer medicines act on the body, there is a chance that they might cause other unwanted effects that may not occur until months or years after the medicine is used. These delayed effects may include certain types of cancer. Discuss these possible effects with your doctor.

Check with your doctor immediately if any of the following side effects occur:

• Less common
  • Black, tarry stools;  blood in urine or stools;  cough or hoarseness;  fever or chills;  lower back or side pain;  painful or difficult urination;  pinpoint red spots on skin;  unusual bleeding or bruising 
  
  

Check with your doctor as soon as possible if any of the following side effects occur:

• More common
  • Unusual tiredness or weakness;  yellow eyes or skin 
  
  

• Less common
  • Joint pain;  loss of appetite;  nausea and vomiting;  swelling of feet or lower legs 
  
  

• Rare
  • Sores in mouth and on lips 
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

• Less common
  • Darkening of skin;  diarrhea;  headache;  skin rash and itching;  weakness 
  
  

After you stop taking mercaptopurine, it may still produce some side effects that need attention. During this period of time, check with your doctor if you notice any of the following side effects:

• Black, tarry stools;  blood in urine or stools;  cough or hoarseness;  fever or chills;  lower back or side pain;  painful or difficult urination;  pinpoint red spots on skin;  unusual bleeding or bruising;  yellow eyes or skin 

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.