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Pronunciation: THIGH-oh-GWAHN-een
Class: Purine analog

Trade Names

- Tablets 40 mg

Lanvis (Canada)


Thioguanine, an analog of the nucleic acid constituent guanine, is closely related structurally and functionally to 6-mercaptopurine. Thioguanine nucleotides are incorporated into RNA and DNA by phosphodiester linkages and incorporation of such fraudulent bases may contribute to the cytotoxicity of thioguanine.

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Thioguanine absorption is incomplete and variable, averaging about 30%. T max is 8 h and C max is seldom over 1 to 2 mcg/mL.


Thioguanine undergoes rapid metabolism to active intracellular derivatives.


Trace quantities of thioguanine are found in urine; some metabolites are found in urine after about 22 h.

Indications and Usage


For remission induction and remission consolidation therapy of acute nonlymphocytic leukemia; busulfan is the preferred drug for treating the chronic phase of chronic myelogenous leukemia.

Unlabeled Uses

Psoriasis; second-line treatment of ulcerative colitis; Crohn disease.


Prior resistance to this drug. There is usually complete cross-resistance between mercaptopurine and thioguanine.

Dosage and Administration

Adults and Children

PO 2 mg/kg/day; if there is no clinical improvement and no leukocyte or platelet depression, the dosage may be cautiously increased to 3 mg/kg/day.

General Advice

  • Follow institutional and NIH procedures for handling, administration, and disposal of anticancer drugs.
  • Administer total daily dose at one time.


Store tablets at controlled room temperature (59° to 77°F). Protect from moisture.

Drug Interactions

Aminosalicylate derivatives (eg, mesalazine, olsalazine, sulphasalazine)

Based on in vitro data, which indicates enzyme inhibition by aminosalicylate derivatives, use with caution.


There is usually complete cross-resistance between mercaptopurine and thioguanine.

Laboratory Test Interactions

None well documented.

Adverse Reactions


Anorexia; intestinal necrosis and perforation (with multiple-drug regimens); nausea; stomatitis; vomiting.




Myelosuppression; pancytopenia (with multiple-drug regimens).


Abnormal liver enzymes; jaundice; liver toxicity associated with vascular endothelial damage (hepatic veno-occlusive disease and/or signs and symptoms of portal hypertension).



Obtain CBC with differential and quantitative platelet count frequently while patient is on thioguanine. Monitor transaminases, alkaline phosphatase, and bilirubin at weekly intervals when initiating therapy and at monthly intervals thereafter. Monitor more frequently in patients with known pre-existing liver disease or in patients receiving other hepatotoxic drugs.


Category D .




Dose selection should be cautious, usually starting at the lower end of the dosing range, reflecting the greater frequency of decreased hepatic and renal function, and comorbidity.

Bone marrow suppression

Most consistent, dose-related toxicity; may be manifested by anemia, leukopenia, thrombocytopenia, or any combination of these. Withdraw thioguanine temporarily at first sign of an abnormally large fall in any of the formed elements of the blood.

Enzyme deficiency

There are patients with inherited deficiency of the enzyme thiopurine methyltransferase (TPMT) who may be unusually sensitive to the myelosuppressive effects of thioguanine and prone to developing rapid bone marrow suppression following initiation of treatment. Substantial dosage reductions may be required to avoid life-threatening bone marrow suppression.


Has occurred. Discontinue in patients with evidence of liver toxicity.


Frequently occurs; ensure risk of developing hyperuricemia is evaluated before starting therapy and that hypouricemic therapy, including adequate fluid intake and monitoring of uric acid, is initiated before starting treatment in patient determined to be at risk for developing hyperuricemia and urate precipitation.

Live vaccines

Do not administer live vaccines to immunocompromised patients.


Not recommended for maintenance therapy or similar long-term continuous treatments because of the risk of liver toxicity.



Azotemia, diaphoresis, hypotension, malaise, myelosuppression, nausea, vomiting.

Patient Information

  • Advise patient, family, or caregiver that medication may be used in combination with other agents, to achieve maximum benefit possible.
  • Advise patient to take as a single daily dose.
  • Advise patient, family, or caregiver to immediately report any of the following to health care provider: rash; hives; difficulty breathing; fever, chills or other signs of infection; bleeding or unusual bruising; sores in mouth or sore throat; persistent nausea, vomiting, and/or appetite loss; dark urine; yellowing of skin or eyes; paleness; general body weakness.
  • Caution women of childbearing potential to avoid becoming pregnant during therapy.

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