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Thioguanine

Medically reviewed on March 25, 2018

Pronunciation

(thye oh GWAH neen)

Index Terms

  • 2-Amino-6-Mercaptopurine
  • 6-TG (error-prone abbreviation)
  • 6-Thioguanine (error-prone abbreviation)
  • TG
  • Tioguanine

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Tablet, Oral:

Tabloid: 40 mg [scored]

Brand Names: U.S.

  • Tabloid

Pharmacologic Category

  • Antineoplastic Agent, Antimetabolite
  • Antineoplastic Agent, Antimetabolite (Purine Analog)

Pharmacology

Thioguanine is a purine analog of guanine that is incorporated into DNA and RNA resulting in the blockage of synthesis and metabolism of purine nucleotides.

Absorption

~30% (range: 14% to 46%; highly variable)

Distribution

Does not reach therapeutic concentrations in the CSF

Metabolism

Hepatic; rapidly and extensively via thiopurine methyltransferase (TPMT) to 2-amino-6-methylthioguanine (MTG; active) and inactive compounds

Excretion

Urine, primarily as metabolites

Time to Peak

Serum: Within 8 hours; predominantly metabolite(s)

Half-Life Elimination

Terminal: 5 to 9 hours

Use: Labeled Indications

Acute myeloid leukemia: Treatment (remission induction and consolidation) of acute myeloid (nonlymphocytic) leukemia (AML)

Limitations of use: The use of thioguanine for AML maintenance therapy or other similar long-term continuous treatments is not recommended due to the high risk of hepatotoxicity.

Off Label Uses

Acute lymphoblastic leukemia (adolescents and adults)

Data from two studies supports the use of thioguanine as a component of combination therapy in late intensification phase in acute lymphoblastic leukemia (ALL) treatment in adolescents 15 years of age and older and adults [Larson 1995], [Larson 1998].

Acute lymphoblastic leukemia (children and adolescents)

Data from two randomized clinical trials in children and adolescents supports the use of thioguanine as part of combination therapy in the delayed intensification treatment phase in acute lymphoblastic leukemia (ALL) in children 1 to 9 years of age [Lange 2002] and in children and adolescents [Nachman 1998].

Contraindications

Prior resistance to thioguanine (or mercaptopurine)

Canadian labeling: Additional contraindications (not in the US labeling): Hypersensitivity to thioguanine or any component of the formulation

Dosing: Adult

Note: Consider testing for thiopurine S-methyltransferase (TPMT) deficiency; patients with TMPT deficiency are at increased risk for severe toxicity at conventional thioguanine doses and generally require dose reduction (Relling 2011).

Acute myeloid leukemia (AML): Oral: 2 mg/kg once daily for 4 weeks; if no clinical improvement after 4 weeks and ANC and platelet counts are not depressed, may increase dose to 3 mg/kg once daily with careful monitoring.

Acute lymphoblastic leukemia (ALL) (off-label use): Oral: Late intensification treatment phase: 60 mg/m2 once daily on days 29 to 42 (in combination with doxorubicin, vincristine, dexamethasone, cyclophosphamide and cytarabine) (Larson 1995; Larson 1998)

Dosage adjustment for TPMT deficiency:

Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines for reduced TPMT activity (Relling 2011; Relling 2013):

Heterozygous deficiency (intermediate activity): Initiate thioguanine with the dose reduced by 30% to 50% of the usual dose and adjust based on the degree of myelosuppression and condition being treated. Allow 2 to 4 weeks after each dosage adjustment to reach steady state. For patients receiving combination therapy who experience severe myelosuppression, the focus should be on reducing the thioguanine dose over other agents (depending on concomitant therapy).

Homozygous deficiency (low or deficient activity): Initiate thioguanine with drastically reduced doses (reduce the daily dose by 10-fold and reduce the frequency from once daily to 3 times per week). Adjust doses based on the degree of myelosuppression and condition being treated. Allow 4 to 6 weeks after each dosage adjustment to reach steady state. For patients receiving combination therapy who experience severe myelosuppression, the focus should be on reducing the thioguanine dose over other agents (depending on concomitant therapy). When used for nonmalignant conditions, consider alternative (non-thiopurine) immunosuppressant therapy.

Homozygous wild type (normal activity): No dosage adjustment necessary. Allow 2 weeks after each dosage adjustment to reach steady state. For patients receiving combination therapy, dosage adjustments (of all agents) should be made without any emphasis on thioguanine compared to other agents.

Dosing: Pediatric

Note: Consider testing for thiopurine S-methyltransferase (TPMT) deficiency; patients with TMPT deficiency are at increased risk for severe toxicity at conventional thioguanine doses and generally require dose reduction (Relling 2011).

Acute myeloid leukemia (AML): Oral: 2 mg/kg once daily for 4 weeks; if no clinical improvement after 4 weeks and ANC and platelet counts are not depressed, may increase dose to 3 mg/kg once daily with careful monitoring.

Acute lymphoblastic leukemia (ALL) (off-label use): Oral:

Children ≥1 year and Adolescents: Delayed intensification treatment phase: 60 mg/m2/day for 14 days on days 28 to 41 (in combination with vincristine, dexamethasone, doxorubicin, cyclophosphamide, cytarabine, asparaginase, and methotrexate) (Lange 2002; Nachman 1998)

Adolescents ≥15 years: Late intensification treatment phase: 60 mg/m2 once daily on days 29 to 42 (in combination with doxorubicin, vincristine, dexamethasone, cyclophosphamide, and cytarabine) (Larson 1995; Larson 1998)

Dosage adjustment for TPMT deficiency:

Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines for reduced TPMT activity (Relling 2011; Relling 2013):

Heterozygous deficiency (intermediate activity): Initiate thioguanine with the dose reduced by 30% to 50% of the usual dose and adjust based on the degree of myelosuppression and condition being treated. Allow 2 to 4 weeks after each dosage adjustment to reach steady state. For patients receiving combination therapy who experience severe myelosuppression, the focus should be on reducing the thioguanine dose over other agents (depending on concomitant therapy).

Homozygous deficiency (low or deficient activity): Initiate thioguanine with drastically reduced doses (reduce the daily dose by 10-fold and reduce the frequency from once daily to 3 times per week). Adjust doses based on the degree of myelosuppression and condition being treated. Allow 4 to 6 weeks after each dosage adjustment to reach steady state. For patients receiving combination therapy who experience severe myelosuppression, the focus should be on reducing the thioguanine dose over other agents (depending on concomitant therapy). When used for nonmalignant conditions, consider alternative (non-thiopurine) immunosuppressant therapy.

Homozygous wild type (normal activity): No dosage adjustment necessary. Allow 2 weeks after each dosage adjustment to reach steady state. For patients receiving combination therapy, dosage adjustments (of all agents) should be made without any emphasis on thioguanine compared to other agents.

Dosing: Renal Impairment

Adults: There are no dosage adjustments provided in the manufacturer’s labeling.

Children: No dosage adjustment required (Aronoff 2007).

Dosing: Hepatic Impairment

Hepatic impairment prior to treatment: There are no dosage adjustments provided in the manufacturer’s labeling.

Hepatotoxicity during treatment: Deterioration in transaminases, alkaline phosphatase or bilirubin, toxic hepatitis, biliary stasis, clinical jaundice, evidence of hepatic sinusoidal obstruction syndrome (veno-occlusive disease), or evidence of portal hypertension: Discontinue treatment.

Extemporaneously Prepared

20 mg/mL (ASHP Standard Concentration) (ASHP 2017)

A 20 mg/mL oral suspension may be prepared in a vertical flow hood with tablets and Ora-Plus and Ora-Sweet or methylcellulose 1% and simple syrup (Aliabadi 2011).

Ora-Plus and Ora-Sweet: Crush fifteen 40 mg thioguanine tablets in a mortar and reduce to a fine powder. Add 5 mL of Ora-Plus in incremental proportions and mix to a uniform paste. Transfer to a graduated amber glass bottle, rinse mortar with Ora-Sweet and add sufficient quantity to make 30 mL. Label "shake well." Stable for 63 days at room temperature.

Methylcellulose and simple syrup: Crush fifteen 40 mg thioguanine tablets in a mortar and reduce to a fine powder. Add 3.33 mL of methylcellulose 1% in incremental proportions and mix to a uniform paste. Transfer to a graduated amber glass bottle, rinse mortar with simple syrup and add sufficient quantity to make 30 mL. Label "shake well." Stable for 63 days at room temperature.

Aliabadi HM, Romanick M, Somayaji V, Mahdipoor P, Lavasanifar A. Stability of compounded thioguanine oral suspensions [published correction appears in Am J Health Syst Pharm. 2011;68(14):1278.]. Am J Health Syst Pharm. 2011;68(10):900-908.21546641

Administration

Oral: Administer orally; total daily dose can be given at one time.

Storage

Store at 15°C to 25°C (59°F to 77°F). Protect from moisture.

Drug Interactions

5-Aminosalicylic Acid Derivatives: May decrease the metabolism of Thiopurine Analogs. Monitor therapy

Anti-TNF Agents: May enhance the adverse/toxic effect of Thiopurine Analogs. Specifically, the risk for T-cell non-Hodgkin's lymphoma (including hepatosplenic T-cell lymphoma) may be increased. Exceptions: Lenalidomide; Pomalidomide; Thalidomide. Monitor therapy

BCG (Intravesical): Immunosuppressants may diminish the therapeutic effect of BCG (Intravesical). Avoid combination

BCG (Intravesical): Myelosuppressive Agents may diminish the therapeutic effect of BCG (Intravesical). Avoid combination

Chloramphenicol (Ophthalmic): May enhance the adverse/toxic effect of Myelosuppressive Agents. Monitor therapy

CloZAPine: Myelosuppressive Agents may enhance the adverse/toxic effect of CloZAPine. Specifically, the risk for neutropenia may be increased. Monitor therapy

Coccidioides immitis Skin Test: Immunosuppressants may diminish the diagnostic effect of Coccidioides immitis Skin Test. Monitor therapy

Deferiprone: Myelosuppressive Agents may enhance the neutropenic effect of Deferiprone. Avoid combination

Denosumab: May enhance the adverse/toxic effect of Immunosuppressants. Specifically, the risk for serious infections may be increased. Monitor therapy

Dipyrone: May enhance the adverse/toxic effect of Myelosuppressive Agents. Specifically, the risk for agranulocytosis and pancytopenia may be increased Avoid combination

Echinacea: May diminish the therapeutic effect of Immunosuppressants. Consider therapy modification

Fingolimod: Immunosuppressants may enhance the immunosuppressive effect of Fingolimod. Management: Avoid the concomitant use of fingolimod and other immunosuppressants when possible. If combined, monitor patients closely for additive immunosuppressant effects (eg, infections). Consider therapy modification

Leflunomide: Immunosuppressants may enhance the adverse/toxic effect of Leflunomide. Specifically, the risk for hematologic toxicity such as pancytopenia, agranulocytosis, and/or thrombocytopenia may be increased. Management: Consider not using a leflunomide loading dose in patients receiving other immunosuppressants. Patients receiving both leflunomide and another immunosuppressant should be monitored for bone marrow suppression at least monthly. Consider therapy modification

Lenograstim: Antineoplastic Agents may diminish the therapeutic effect of Lenograstim. Management: Avoid the use of lenograstim 24 hours before until 24 hours after the completion of myelosuppressive cytotoxic chemotherapy. Consider therapy modification

Lipegfilgrastim: Antineoplastic Agents may diminish the therapeutic effect of Lipegfilgrastim. Management: Avoid concomitant use of lipegfilgrastim and myelosuppressive cytotoxic chemotherapy. Lipegfilgrastim should be administered at least 24 hours after the completion of myelosuppressive cytotoxic chemotherapy. Consider therapy modification

Natalizumab: Immunosuppressants may enhance the adverse/toxic effect of Natalizumab. Specifically, the risk of concurrent infection may be increased. Avoid combination

Nivolumab: Immunosuppressants may diminish the therapeutic effect of Nivolumab. Consider therapy modification

Ocrelizumab: May enhance the immunosuppressive effect of Immunosuppressants. Monitor therapy

Palifermin: May enhance the adverse/toxic effect of Antineoplastic Agents. Specifically, the duration and severity of oral mucositis may be increased. Management: Do not administer palifermin within 24 hours before, during infusion of, or within 24 hours after administration of myelotoxic chemotherapy. Consider therapy modification

Pidotimod: Immunosuppressants may diminish the therapeutic effect of Pidotimod. Monitor therapy

Pimecrolimus: May enhance the adverse/toxic effect of Immunosuppressants. Avoid combination

Promazine: May enhance the myelosuppressive effect of Myelosuppressive Agents. Monitor therapy

Roflumilast: May enhance the immunosuppressive effect of Immunosuppressants. Consider therapy modification

Sipuleucel-T: Immunosuppressants may diminish the therapeutic effect of Sipuleucel-T. Monitor therapy

Tacrolimus (Topical): May enhance the adverse/toxic effect of Immunosuppressants. Avoid combination

Tertomotide: Immunosuppressants may diminish the therapeutic effect of Tertomotide. Monitor therapy

Tofacitinib: Immunosuppressants may enhance the immunosuppressive effect of Tofacitinib. Management: Concurrent use with antirheumatic doses of methotrexate or nonbiologic disease modifying antirheumatic drugs (DMARDs) is permitted, and this warning seems particularly focused on more potent immunosuppressants. Consider therapy modification

Trastuzumab: May enhance the neutropenic effect of Immunosuppressants. Monitor therapy

Vaccines (Inactivated): Immunosuppressants may diminish the therapeutic effect of Vaccines (Inactivated). Management: Vaccine efficacy may be reduced. Complete all age-appropriate vaccinations at least 2 weeks prior to starting an immunosuppressant. If vaccinated during immunosuppressant therapy, revaccinate at least 3 months after immunosuppressant discontinuation. Consider therapy modification

Vaccines (Live): Immunosuppressants may enhance the adverse/toxic effect of Vaccines (Live). Immunosuppressants may diminish the therapeutic effect of Vaccines (Live). Management: Avoid use of live organism vaccines with immunosuppressants; live-attenuated vaccines should not be given for at least 3 months after immunosuppressants. Avoid combination

Adverse Reactions

Frequency not defined.

Cardiovascular: Esophageal varices, portal hypertension

Endocrine & metabolic: Fluid retention, hyperuricemia (common), weight gain

Gastrointestinal: Anorexia, intestinal necrosis, intestinal perforation, nausea, stomatitis, vomiting

Hematologic & oncologic: Anemia (may be delayed), bone marrow hypoplasia, granulocytopenia, hemorrhage, leukopenia (common; may be delayed), pancytopenia, splenomegaly, thrombocytopenia (common; may be delayed)

Hepatic: Ascites, hepatic necrosis (centrilobular), hepatic sinusoidal obstruction syndrome (formerly known as hepatic veno-occlusive disease), hepatitis, hepatomegaly (tender), hepatotoxicity, hyperbilirubinemia, increased liver enzymes, jaundice

Infection: Infection

Warnings/Precautions

Concerns related to adverse effects:

• Bone marrow suppression: Myelosuppression (anemia, leukopenia, and/or thrombocytopenia) is a common dose-related toxicity (may be delayed); monitor for infection (due to leukopenia) or bleeding (due to thrombocytopenia); withhold treatment with abnormally significant drop in blood counts. Patients with genetic enzyme deficiency of thiopurine methyltransferase (TPMT) or who are receiving drugs which inhibit this enzyme (mesalazine, olsalazine, sulfasalazine) may be highly sensitive to myelosuppressive effects and may require substantial dose reductions.

• Hepatotoxicity: Long-term continuous therapy or maintenance treatment is associated with a high risk for hepatotoxicity, hepatic sinusoidal obstruction syndrome (SOS; formerly called veno-occlusive disease [VOD]), or portal hypertension. Monitor liver function carefully for liver toxicity and discontinue in patients with evidence of hepatotoxicity, hepatic SOS (eg, hyperbilirubinemia, hepatomegaly [tender], and weight gain due to ascites and fluid retention) or portal hypertension (eg, splenomegaly, thrombocytopenia, esophageal varices). Hepatotoxicity with or without transaminase elevations may occur. Pathologic findings of hepatotoxicity include hepatoportal sclerosis, idiopathic noncirrhotic portal hypertension (including nodular regenerative hyperplasia), peliosis hepatitis, and periportal fibrosis. Hepatotoxicity may be more prevalent in male patients. Long-term/maintenance treatment with thioguanine is not recommended. Advise patients to avoid alcohol; may increase the risk for hepatotoxicity.

• Secondary malignancies: Thioguanine is potentially carcinogenic.

• Tumor lysis syndrome: Hyperuricemia occurs commonly with treatment; institute adequate hydration and prophylactic allopurinol.

Disease-related concerns:

• Thiopurine S methyltransferase deficiency: Patients with genetic enzyme deficiency of thiopurine S methyltransferase (TPMT) may be sensitive to myelosuppressive effects. May require substantial dose reductions. Consider testing for TPMT deficiency; guidelines from the Clinical Pharmacogenetics Implementation Consortium (CPIC) for reduced TPMT activity recommend dose reductions for patients with heterozygous activity or homozygous deficiency (Relling 2011; Relling 2013).

Concurrent drug therapy issues:

• Drug-drug interactions: Potentially significant interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information.

Other warnings/precautions:

• Appropriate use: Not recommended for maintenance therapy or long term continuous treatment due to toxicities.

• Cross resistance: Cross resistance with mercaptopurine generally occurs.

• Vaccines: Avoid vaccination with live vaccines during treatment.

Monitoring Parameters

CBC with differential and platelet count (frequently); liver function tests (weekly when beginning therapy then monthly, more frequently in patients with liver disease or concurrent hepatotoxic drugs); serum uric acid; consider testing for thiopurine S-methyltransferase (TPMT) deficiency.

Monitor for signs/symptoms of hepatotoxicity, portal hypertension (splenomegaly, esophageal varices, thrombocytopenia), or sinusoidal obstruction syndrome (veno-occlusive disease; fluid retention, ascites, hepatomegaly with tenderness, or hyperbilirubinemia); monitor for tumor lysis syndrome. Monitor adherence.

Pregnancy Risk Factor

D

Pregnancy Considerations

Adverse effects have been observed in animal reproduction studies. May cause fetal harm if administered during pregnancy. Females of reproductive potential should avoid becoming pregnant during treatment.

Patient Education

• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Patient may experience nausea, vomiting, lack of appetite, or mouth sores. Have patient report immediately to prescriber signs of infection, signs of liver problems (dark urine, fatigue, lack of appetite, nausea, abdominal pain, light-colored stools, vomiting, or jaundice), signs of bleeding (vomiting blood or vomit that looks like coffee grounds; coughing up blood; hematuria; black, red, or tarry stools; bleeding from the gums; abnormal vaginal bleeding; bruises without a reason or that get bigger; or any severe or persistent bleeding), severe loss of strength and energy, abdominal edema, excessive weight gain, or signs of tumor lysis syndrome (tachycardia or abnormal heartbeat; any passing out; urinary retention; muscle weakness or cramps; nausea, vomiting, diarrhea or lack of appetite; or feeling sluggish) (HCAHPS).

• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for health care professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience, and judgment in diagnosing, treating, and advising patients.

Further information

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