thioguanine (Rx)

Brand and Other Names:6TG, 6Thioguanine, more...Tabloid
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Dosing & Uses

AdultPediatric

Dosage Forms & Strengths

tablet

  • 40mg

Acute Nonlymphocytic Leukemia

2 mg/kg/day PO  

Cautiously increase to 3 mg/kg/day if no response after 4 weeks

May be used in multi-drug therapy, including prednisone, cytarabine, cyclophosphamide, vincristine

Monitor: CBC, LFTs

Take on empty stomach to reduce risk of nausea and vomiting

Dosage Forms & Strengths

tablet

  • 40mg

Acute Nonlymphocytic Leukemia

2 mg/kg/day PO  

Cautiously increase to 3 mg/kg/day if no response after 4 weeks

May be used in multi-drug therapy, including prednisone, cytarabine, cyclophosphamide, vincristine

Monitor: CBC, LFTs

Take on empty stomach to reduce risk of nausea and vomiting

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Interactions

Interaction Checker

and thioguanine

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            Adverse Effects

            Frequency Not Defined

            Anorexia

            Stomatitis

            Vomiting

            Nausea

            Myelosuppression

            Hyperuricemia

            Nephrotoxicity

            Hepatotoxicity

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            Warnings

            Contraindications

            Hypersensitivity; prior resistance to 6-thioguanine or mercaptopurine

            Cautions

            Therapy should be administered only by physicians experienced with the risks of therapy and with knowledge on the natural history of acute nonlymphocytic leukemias

            Long-term continuous therapy associated with high risk for hepatotoxicity, portal hypertension, or sinusoidal obstruction syndrome; monitor liver function closely and discontinue therapy if patient experiences symptoms of hepatotoxicity, including hyperbilirubinemia, hepatomegaly, portal hypertension such as thrombocytopenia out of proportion with neutropenia and splenomegaly; elevations of liver enzymes have also been reported in association with liver toxicity but do not always occur

            The most consistent, dose-related toxicity is bone marrow suppression, which may be manifested by anemia, leukopenia, thrombocytopenia, or any combination of these; any one of these findings may also reflect progression of underlying disease; since thioguanine may have a delayed effect, it is important to withdraw medication temporarily at first sign of an abnormally large fall in any of formed elements of blood

            Evaluate patients with repeated severe myelosuppression for thiopurine S-methyltransferase (TPMT) or nucleotide diphosphatase (NUDT15) deficiency; TPMT genotyping or phenotyping (red blood cell TPMT activity) and NUDT15 genotyping can identify patients who have reduced activity of these enzymes; patients with homozygous TPMT or NUDT15 deficiency require substantial dosage reductions; bone marrow suppression could be exacerbated by co-administration with drugs that inhibit TPMT, such as olsalazine, mesalazine, or sulphasalazine

            Obtain evaluation of the hemoglobin concentration or hematocrit, total white blood cell count and differential count, and quantitative platelet count frequently while on thioguanine therapy; in cases where cause of fluctuations in formed elements in peripheral blood is obscure, bone marrow examination may be useful for evaluation of marrow status; the decision to increase, decrease, continue, or discontinue a given dosage of thioguanine must be based not only on the absolute hematologic values, but also upon rapidity with which changes are occurring; in many instances, particularly during induction phase of acute leukemia, complete blood counts will need to be done more frequently in order to evaluate effect of therapy; dosage of thioguanine may need to be reduced when combined wi

            Myelosuppression is often unavoidable during induction phase of adult acute nonlymphocytic leukemias if remission induction is to be successful; whether or not this demands modification or cessation of dosage depends both upon response of underlying disease and a careful consideration of supportive facilities (granulocyte and platelet transfusions) which may be available; life-threatening infections and bleeding have been observed as consequences of thioguanine-induced granulocytopenia and thrombocytopenia

            Therapy is potentially carcinogenic

            Institute adequate hydration and administer allopurinol prophylactically to minimize risk of hyperuricemia, which commonly occurs with treatment

            Monitor for infections (leukopenia)

            Monitor for bleeding (thrombocytopenia)

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            Pregnancy & Lactation

            Pregnancy Category: D

            Lactation: not known if excreted in breast milk, do not nurse

            Pregnancy Categories

            A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.

            B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

            C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.

            D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.

            X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.

            NA: Information not available.

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            Pharmacology

            Mechanism of Action

            Purine analog that is incorporated into DNA and RNA and inhibits purine ribonucleotide synthesis

            Pharmacokinetics

            Half-Life: 15 min (initial phase); 5-9 hr (terminal phase)

            Absorption: 30%

            Time to peak: 8hr (serum)

            Metabolism: Liver

            Metabolites: 2-amino-6-methylthiopurine, inorganic sulfate, thiouric acid

            Excretion: Urine

            Dialyzable: No

            Pharmacogenomics

            Converted via thiopurine S-methyltransferase (TPMT) to 2-amino-6-methylthioguanine (MTG, active metabolite) and inactive metabolites

            Complete TPMT deficiency is rare in the general population (0.3%); increased myelosuppression when used with TPMT deficiency

            Alleles associated with decreased TPMT enzymatic activity are TPMT*2, TPMT*3A, and TPMT*3C

            Companies providing genetic testing

            • The following companies currently offer testing for TPMT variants
            • Prometheus Labs (http://www.prometheuslabs.com/)
            • Arup Laboratories (http://www.aruplab.com/)
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            Formulary

            FormularyPatient Discounts

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            Tier Description
            1 This drug is available at the lowest co-pay. Most commonly, these are generic drugs.
            2 This drug is available at a middle level co-pay. Most commonly, these are "preferred" (on formulary) brand drugs.
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            5 This drug is available at a higher level co-pay. Most commonly, these are "non-preferred" brand drugs or specialty prescription products.
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            Medscape prescription drug monographs are based on FDA-approved labeling information, unless otherwise noted, combined with additional data derived from primary medical literature.