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Action/Kinetics:
Cell-cycle specific for the S phase of cell division. Converted to thioinosinic acid by the enzyme hypoxanthine-guanine phosphoribosyltransferase. Thioinosinic acid then inhibits reactions involving inosinic acid. Also, both thioinosinic acid and 6-methylthioinosinate (also formed from mercaptopurine) inhibit RNA synthesis. About 50% absorbed from GI tract.
Plasma t
1/2: 47 min in adults and 21 min in children. Metabolites are excreted in urine with up to 39% excreted unchanged. Cross-resistance with thioguanine has been observed.
Uses:
Acute lymphocytic or myelocytic leukemia. Lymphoblastic leukemia, especially in children. Acute myelogenous and myelomonocytic leukemia. Effectiveness varies depending on use. The drug is not effective for leukemia of the CNS, solid tumors, lymphomas, or chronic lymphatic leukemia.
Investigational: Inflammatory bowel disease, chronic myelocytic leukemia, polycythemia vera, non-Hodgkin's lymphoma, psoriatic arthritis.
Contraindications:
Use in resistance to mercaptopurine or thioguanine. To treat CNS leukemia, chronic lymphatic leukemia, lymphomas (including Hodgkin's disease), solid tumors. Lactation.
Special Concerns:
Use with caution in clients with impaired renal function. Use during lactation only if benefits clearly outweigh risks. Severe bone marrow depression (anemia, leukopenia, thrombocytopenia) may occur. There is an increased risk of pancreatitis when used for inflammatory bowel disease.
Additional Side Effects:
Hepatotoxicity, oral lesions, drug fever, hyperuricemia. Produces less GI toxicity than folic acid antagonists, and side effects are less frequent in children than in adults. Pancreatitis (when used for inflammatory bowel disease).
Overdose Management:
Symptoms: Immediate symptoms include N&V;, diarrhea, and anorexia while delayed symptoms include myelosuppression, gastroenteritis, and liver dysfunction.
Treatment: Induction of emesis if detected soon after ingestion. Supportive measures.
Drug Interactions:
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Allopurinol /
Methotrexate effect R/T
liver breakdown (reduce methotrexate dose by 25%-33%)
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Trimethoprim-Sulfamethoxazole /
Risk of bone marrow suppression
How Supplied:
Tablet: 50 mg
Dosage
?Tablets
Highly individualized: 2.5 mg/kg/day.
Adults, usual: 100-200 mg;
pediatric: 50 mg. Dosage may be increased to 5 mg/kg/day after 4 weeks if beneficial effects are not noted. Dosage is increased until symptoms of toxicity appear.
Maintenance after remission: 1.5-2.5 mg/kg/day.
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