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Thioguanine is an anticancer (antineoplastic) agent belonging to the class of drugs called antimetabolites. It also acts as a suppressor of the immune system. It is available only in the generic form in the United States, or under the brand name Lanvis in Canada. Other common designations for thioguanine include 6-thioguanine (6-TG) and TG.


Thioguanine is used to treat various forms of acute and nonlymphocytic leukemias. It is usually used in combination with other chemotherapy drugs, such as cyclophosphamide , cytarabine , prednisone, and/or vincristine .


Thioguanine chemically interferes with the synthesis of genetic material of cancer cells. It acts as a false building block for DNA and RNA, which, when used to copy DNA and RNA, leads to cell death.

Recommended dosage

Thioguanine is administered orally. It is generally given once per day in a dosage of 2 mg per kg (2.2 pounds) of body weight. This dosage may be increased to 3 mg per kg if the patient does not respond to the medication within three weeks.


Thioguanine can cause an allergic reaction in some people. Patients with a prior allergic reaction to thiogua-nine or mercaptopurine should not take thioguanine.

Thioguanine can cause serious birth defects if either the man or the woman is taking this drug at the time of conception or if the woman is taking this drug during pregnancy. Because thioguanine is easily passed from mother to child through breast milk, breast feeding is not recommended while thioguanine is being taken.

This drug suppresses the immune system and interferes with the normal functioning of certain organs and tissues. For these reasons, it is important that the prescribing physician is aware of any of the following preexisting medical conditions:

  • a current case of, or recent exposure to, chicken pox
  • herpes zoster (shingles)
  • a current case, or history of, gout or kidney stones
  • all current infections
  • kidney disease
  • liver disease

Also, because thioguanine is such a potent immunosuppressant, patients receiving this drug must exercise extreme caution to avoid contracting any new infections, and should make an effort to:

  • avoid any individual with any type of infection
  • avoid bleeding injuries, including those caused by brushing or flossing the teeth
  • avoid contact of the hands with the eyes or nasal passages
  • avoid contact sports or any other activity that could cause a bruising or bleeding injury

Side effects

A common side effect of thioguanine use is myelo-suppression with decreases in white blood cell and platelet counts. Other possible side effects include:

  • increased susceptibility to infection
  • nausea and vomiting
  • diarrhea
  • mouth sores
  • skin rash, itching , or hives
  • swelling in the feet or lower legs

A doctor should be consulted immediately if the patient experiences:

  • black, tarry or bloody stools
  • blood in the urine
  • persistent cough
  • fever and chills
  • pain in the lower back or sides
  • painful or difficult urination
  • unusual bleeding or bruising


Thioguanine should not be taken in combination with any prescription drug, over-the-counter drug, or herbal remedy without prior consultation with a physician. It is particularly important that the prescribing physician be aware of the use of any of the following drugs:

  • antithyroid agents
  • azathioprine
  • chloramphenicol
  • colchicine
  • flucytosine
  • interferon
  • plicamycin
  • probenecid
  • sulfinpyrazone
  • zidovudine
  • any radiation therapy or chemotherapy medicines

See Also Cancer genetics; Chemoprevention; DNA flow cytometry; Drug resistance

Paul A. Johnson, Ed.M.



A drug that prevents the growth of a neoplasm by interfering with the maturation or proliferation of the cells of the neoplasm.


New abnormal growth of tissue.

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thioguanine (th'y-oh-gwah-neen) n. see tioguanine.

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