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Precautions and Warnings With Thioguanine

Thioguanine may increase your risk of developing other types of cancer or bone marrow depression. To help ensure your safety, talk to your healthcare provider about your medical history before starting treatment with thioguanine. Other warnings and precautions with this chemotherapy medicine apply to people who have liver disease, those who are taking certain medications, and women who are pregnant or nursing.

What Should I Tell My Healthcare Provider?

You should talk with your healthcare provider prior to taking thioguanine (Tabloid®) if you have:
  • Liver disease, such as hepatitis, cirrhosis, or liver failure
  • Kidney disease, such as kidney failure (renal failure)
  • Been previously treated with thioguanine or a medication known as mercaptopurine (Purinethol®)
  • Been told you have thiopurine-S-methyltransferase (TPMT) deficiency or a defect in the TPMT gene
  • Plans to receive a vaccination
  • Plans for surgery or dental work
  • An infection
  • Any allergies, including 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 Thioguanine Precautions and Warnings

Some warnings and precautions to be aware of prior to taking this medication include the following:
  • Thioguanine is a potent anticancer medication associated with potentially serious side effects. It should only be prescribed by healthcare providers experienced in using the medication.
  • Thioguanine has been reported to cause liver damage, especially when used continuously for long periods of time. Therefore, it should not be used for maintenance treatment of leukemia, or any other long-term treatment. Your healthcare provider will monitor you frequently during treatment for liver problems. Stop taking the medication and contact your healthcare provider immediately if you develop yellowing of the skin or whites of the eyes (jaundice), which could be a sign of liver damage.  
  • You should know that this medication may increase your risk for developing other cancers.
  • Thioguanine can cause significant bone marrow suppression (when the bone marrow is unable to produce adequate amounts of blood cells), which may increase your risk for potentially serious infections (due to low white blood cells), anemia (due to low red blood cells), and bleeding problems (due to low platelets). Your healthcare provider will monitor your blood cell counts closely during treatment. 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
    • 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.
  • People with an inherited defect in a certain gene known as the thiopurine-S-methyltransferase (TPMT) gene may be especially sensitive to bone marrow suppression from thioguanine, and may need lower-than-usual thioguanine doses. Your healthcare provider may choose to test you for this gene, or check your TPMT activity with a blood test, and reduce your thioguanine dose if necessary. 
  • Cancer that is resistant to a medication known as mercaptopurine (Purinethol®) is also usually resistant to thioguanine. Make sure your healthcare provider knows if you have previously been treated with mercaptopurine.
  • Thioguanine 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 Tabloid and Pregnancy).
  • It is unknown if thioguanine passes through breast milk. If you are breastfeeding or plan to start, discuss this with your healthcare provider prior to taking thioguanine (see Tabloid and Breastfeeding).
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