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Thioguanine

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

Brand Names: U.S.

  • Tabloid

Pharmacologic Category

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

Pharmacology

Purine analog 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: 5-9 hours

Use: Labeled Indications

Treatment of acute myelogenous (nonlymphocytic) leukemia (AML)

Use: Unlabeled

Treatment of pediatric acute lymphoblastic leukemia (ALL)

Contraindications

Prior resistance to thioguanine (or mercaptopurine)

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

Dosing: Pediatric

Pediatric ALL (off-label use; combination therapy): Oral: Delayed intensification treatment phase: 60 mg/m2/day for 14 days (Lange, 2002; Nachman, 1998)

Dosing: Renal Impairment

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

Children: No adjustment required (Aronoff, 2007).

Dosing: Hepatic Impairment

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

Hazardous agent: Use appropriate precautions for handling and disposal (NIOSH 2014 [group 1]).

A 20 mg/mL oral suspension may be made with tablets, methylcellulose 1%, and simple syrup NF. Crush fifteen 40 mg tablets in a mortar and reduce to a fine powder. Add 10 mL methylcellulose 1% in incremental proportions and mix to a uniform paste. Transfer to a graduated cylinder, rinse mortar with simple syrup, and add quantity of simple syrup sufficient to make 30 mL. Label "shake well" and "refrigerate". Stable for 84 days refrigerated (preferred) or at room temperature.

Dressman JB and Poust RI, “Stability of Allopurinol and Five Antineoplastics in Suspension,” Am J Hosp Pharm, 1983, 40(4):616-8. 6846371Nahata MC, Pai VB, and Hipple TF, Pediatric Drug Formulations, 5th ed, Cincinnati, OH: Harvey Whitney Books Co, 2004.

Administration

Administer orally; total daily dose can be given at one time. Hazardous agent; use appropriate precautions for handling and disposal (NIOSH 2014 [group 1]).

Storage

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

Drug Interactions

5-ASA Derivatives: May decrease the metabolism of Thiopurine Analogs. 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

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

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

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

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

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. Avoid combination

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.

Endocrine & metabolic: Fluid retention, hyperuricemia (common)

Gastrointestinal: Anorexia, intestinal necrosis, intestinal perforation, nausea, splenomegaly, stomatitis, vomiting, weight gain

Hematologic: Anemia (may be delayed), bleeding, granulocytopenia, leukopenia (common; may be delayed), marrow hypoplasia, pancytopenia, thrombocytopenia (common; may be delayed)

Hepatic: Ascites, esophageal varices, hepatic necrosis (centrilobular), hepatic sinusoidal obstruction syndrome (SOS; veno-occlusive disease), hepatitis, hepatomegaly [tender], hepatoportal sclerosis, hepatotoxicity, hyperbilirubinemia, jaundice, LFTs increased, nodular regenerative hyperplasia, peliosis hepatitis, periportal fibrosis, portal hypertension

Miscellaneous: 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 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, nodular regenerative hyperplasia, peliosis hepatitis, and periportal fibrosis. 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 methyltransferase deficiency: Patients with genetic enzyme deficiency of thiopurine methyltransferase (TPMT) may be sensitive to myelosuppressive effects. May require substantial dose reductions.

Special handling:

• Hazardous agent: Use appropriate precautions for handling and disposal (NIOSH 2014 [group 1]).

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; liver function tests (weekly when beginning therapy then monthly, more frequently in patients with liver disease or concurrent hepatotoxic drugs); serum uric acid; some laboratories offer testing for TPMT deficiency

Hepatotoxicity may present with signs of portal hypertension (splenomegaly, esophageal varices, thrombocytopenia) or sinusoidal obstruction syndrome (veno-occlusive disease; fluid retention, ascites, hepatomegaly with tenderness, or hyperbilirubinemia)

Pregnancy Risk Factor

D

Pregnancy Considerations

Animal studies have demonstrated adverse effects. There are no adequate and well-controlled studies in pregnant women. May cause fetal harm if administered during pregnancy. Women of childbearing 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 lack of appetite. Have patient report immediately to prescriber signs of infection, signs of hepatic impairment, severe diarrhea, considerable nausea, significant stomatitis, ecchymosis, hemorrhaging, intolerable asthenia, severe edema, excessive weight gain, or signs of tumor lysis syndrome (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 healthcare 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.

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