Cancer Home > Precautions and Warnings With Mercaptopurine

If you have hepatitis, kidney failure, or inflammatory bowel disease, talk to your healthcare provider about potential warnings and precautions that may apply to you before beginning treatment with mercaptopurine. This chemotherapy treatment may not be the best option for some people, including those who are taking certain medications or who have certain allergies. Risks may also apply to women who are pregnant or nursing.

What Should I Tell My Healthcare Provider?

You should talk with your healthcare provider prior to taking mercaptopurine (Purinethol®) if you have:
  • Liver disease, such as hepatitis, cirrhosis, or liver failure
  • Kidney disease, such as kidney failure (renal failure)
  • Been previously treated with mercaptopurine or a medicine known as thioguanine (Tabloid®)
  • Been told you have thiopurine-S-methyltransferase (TPMT) deficiency or a defect in the TPMT gene
  • Inflammatory bowel disease, such as Crohn's disease or ulcerative colitis
  • Plans to receive a vaccination
  • Any allergies, including allergies to foods, dyes, or preservatives.
Also, let your healthcare provider know if you are:
  • Pregnant or thinking of becoming pregnant
  • Breastfeeding.
You should also tell your healthcare provider about all other medications you are taking, including prescription and nonprescription medicines, vitamins, and herbal supplements.

Specific Mercaptopurine Precautions and Warnings

Some warnings and precautions to be aware of prior to taking this medication include the following:
  • Mercaptopurine is a potent anticancer medication associated with potentially serious side effects. It should only be prescribed by a healthcare provider with experience using this drug and assessing response to chemotherapy.
  • You will need regular blood tests during treatment to make sure the medication is working, and to check for potentially serious side effects. Your healthcare provider may need to adjust your dose frequently based on your response to treatment.
  • This medication may increase the risk for developing cancer. There have been reports of a rare but serious cancer known as hepatosplenic lymphoma T-cell lymphoma occurring in people being treated with mercaptopurine for inflammatory bowel disease (such as Crohn's disease or ulcerative colitis). At this time, it is unknown whether mercaptopurine is safe or effective for people with inflammatory bowel disease.
  • Mercaptopurine can cause bone marrow suppression (when the bone marrow is unable to produce adequate amounts of blood cells), which can lead to abnormally low white blood cells, red blood cells, and platelets. As a result, you will have an increased risk for potentially serious infections, anemia, and bleeding problems. Let your healthcare provider know if you have signs of bone marrow suppression, such as:
    • Signs of low platelets, such as:
      • Any abnormal bleeding or bruising
      • Blood in your urine or stools
      • Black, tarry stools
      • Small red or purple spots under the skin
    • Signs of anemia, such as:
      • Fatigue
      • Weakness
      • Shortness of breath
      • Pale skin
    • Signs of infection, such as:
      • Fever
      • Chills
      • Sore throat
      • Cough or shortness of breath
      • Burning or pain when urinating.
  • Some people have an inherited defect in a certain gene known as the thiopurine-S-methyltransferase (TPMT) gene. This defect causes low activity of an enzyme in the body known as TPMT. People with low TPMT activity are more likely to develop rapid bone marrow suppression when starting mercaptopurine treatment, and may need lower-than-normal mercaptopurine doses. Your healthcare provider can test you for this gene, or check your TPMT activity with a blood test, and reduce your mercaptopurine dose if necessary. 
  • This medication may cause liver damage, especially in doses higher than the usual recommended dose. Your healthcare provider will perform blood tests to monitor your liver function throughout treatment. Let him or her know if you have any signs of liver problems, such as:
    • Yellowing of the skin or whites of the eyes
    • Upper-right abdominal (stomach) pain
    • Loss of appetite.
  • Mercaptopurine is eliminated from the body by the kidneys. Therefore, people who have kidney disease may eliminate the drug more slowly and may need lower doses.  
  • Cancer that is resistant to a medication known as thioguanine is also usually resistant to mercaptopurine. Make sure your healthcare provider knows if you have been treated with thioguanine.
  • Mercaptopurine is a pregnancy Category D medication, which means it may harm an unborn child. Talk to your healthcare provider about the risks and benefits of using this medication during pregnancy (see Purinethol and Pregnancy).
  • It is unknown if mercaptopurine passes through breast milk. Therefore, if you are breastfeeding or plan to start, discuss this with your healthcare provider prior to taking mercaptopurine (see Purinethol and Breastfeeding).
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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