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Mercaptopurine is a medicine used to prevent the formation and spread of cancer cells.


Mercaptopurine is used as part of the consolidation and maintenance treatment for acute lymphocytic leukemia (ALL) and acute myelocytic leukemia (AML).


Mercaptopurine (6-mercaptopurine, or 6-MP) is an analog of purine, a component of DNA/RNA, and belongs to antimetabolites that prevent the biosynthesis, or utilization, of normal cellular metabolites. It has been used for several decades in combination with other chemotherapy drugs for the treatment of different types of acute adult and childhood leukemias (ALL and AML). It has also been shown to be effective for the treatment of inflammatory bowel disease (IBD) (which includes Crohn's disease and ulcerative colitis), certain types of arthritis, and polycythemia vera (above normal increase in red cells in the blood). Mercaptopurine helps to decrease the dose of steroids in patients with IBD, and to reduce their dependence on steroids to control symptoms of their disease. The medicine is available under the brand name of Purinethol. It is taken up by red cells in the blood and works by decreasing the formation of certain genetic material (DNA and RNA) in patients with cancer and by altering the activity of the immune system in patients with IBD.

Recommended dosage

Doses vary between different chemotherapy protocols. The usual dose is 2.5 mg per kg (2.2 pounds) per day in adults and children (50 mg daily in an average 5-year old child or 100-200 mg daily in adults). The total daily dose is calculated to the nearest multiple of 25 mg and is given all at one time. Another way of dosing 6-MP is based on body surface area (BSA), and is usually 75 mg per square meter in children and 80-100 mg per square meter in adults.

Doses of 1.5-2.5 mg per kg per day is recommended for leukemia patients. For those patients with inflammatory bowel disease, doses of 1.5 mg per kg per day have been used in research studies.


This medicine is usually taken by mouth and should be given at the same time every day, preferably on an empty stomach (one hour before meals or two hours after meals). Children with leukemia should be taking this medicine at bedtime for maximum effectiveness. All patients should drink plenty of fluids (at least eight glasses of water per day) while taking this medication, unless otherwise directed by a physician.


The use of 6-MP in pregnant women should be avoided whenever possible, especially during the first three months of pregnancy, as 6-MP can cause birth defects and spontaneous abortions.

As 6-MP can lower the body's ability to fight infections, patients are advised to avoid contact with people who have a cold, flu, or other infections.

Mercaptopurine should be used with caution in the following populations:

  • people who had an allergic reaction to 6-MP in the past
  • people at risk for pancreatitis (inflammation of the pancreas)
  • breastfeeding mothers (it is not known if 6-MP crosses in to breast milk)
  • people with liver or kidney disease
  • people with gout (6-MP can exacerbate the symptoms of gout)
  • people taking allopurinol for gout
  • people with suppressed bone marrow (tissue filling the empty spaces inside the bone)

Patients are encouraged to stop taking 6-MP, and contact a physician immediately, if any of the following symptoms develop:

  • fever , chills, or sore throat
  • yellowing of the skin or eyes
  • blood in the urine or stools
  • black stools
  • unusual bleeding or bruising
  • stomach pain with nausea, vomiting, or loss of appetite.

Patients taking 6-MP must see a physician before starting medication therapy, and also occasionally during therapy, to have blood tests for the monitoring of a complete blood count and kidney and liver functions.

Side effects

This is a very potent medicine that can cause serious side effects. These side effects include skin rash, nausea, vomiting, diarrhea , mouth sores, yellowing of the eyes or skin, clay-colored stools, dark urine, decreased ability to fight infections, pinpoint red dots on the skin, and darkening of the skin. Nausea and vomiting , diarrhea, and stomach pain are less common in children than in adults.


Mercaptopurine can decrease the effectiveness of blood thinners such as warfarin (Coumadin).

The drug can exacerbate the symptoms of gout. The anti-gout medication, allopurinol, can increase blood levels of 6-MP and increase the risk of its side effects. The dose of 6-MP needs to be decreased, or its use should be avoided, in patients taking allopurinol, which interferes with the degradation of 6-MP.

Risk of liver disease may be increased in patients taking both doxorubicin (a cancer chemotherapy drug) and 6-MP. Other medicines that decrease the function of the liver can cause increased toxicity with 6-MP. Patients should inform their doctor or pharmacist about all the prescription drugs and over-the-counter medications that they are taking.

Olga Bessmertny, Pharm.D.


Consolidation therapy

A stage in treatment of acute lymphocytic leukemia (ALL) that follows induction of remission. The purpose of this stage is to eliminate remaining cancer cells that cannot be detected by usual methods.

Inflammatory bowel disease (IBD)

This disease can be divided into two types: Crohn's disease and ulcerative colitis. Patients with Crohn's disease can have inflammation of the full thickness of the walls of the entire gastrointestinal tract. In patients with ulcerative colitis, the inflammation is limited to the surface of the walls of the large intestine and rectum.


A type of cancer caused by a progressive increase in abnormal blood-forming cells of the bone marrow.

Maintenance therapy

The last stage in treatment of ALL. The purpose of this stage is to provide long-term exposure to lower doses of drugs and to give the immune system time to kill the leukemia cells.

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mercaptopurine (mer-kap-tŏ-pewr-een) n. a drug that prevents the growth of cancer cells and is administered by mouth, chiefly in the treatment of some types of leukaemia (see antimetabolite). Trade name: Puri-Nethol.