Mercaptopurine
Indications
Mercaptopurine is indicated for maintenance therapy of acute lymphatic (lymphocytic, lymphoblastic) leukemiaas part of a combination regimen. The response to this agent depends upon the particular subclassification of acute lymphatic leukemia and the age of the patient (pediatric or adult).
Mercaptopurine is not effective for prophylaxis or treatment of central nervous system leukemia. Mercaptopurine is not effective in acute myelogenous leukemia, chronic lymphatic leukemia, the lymphomas (including Hodgkins Disease), or solid tumors.
Mercaptopurine is not effective for prophylaxis or treatment of central nervous system leukemia. Mercaptopurine is not effective in acute myelogenous leukemia, chronic lymphatic leukemia, the lymphomas (including Hodgkins Disease), or solid tumors.
Pharmacology
Mercaptopurine is a purine antagonist which is converted intracellularly into its active nucleotides, including thioinosinic acid. The nucleotides inhibit several reactions which ultimately interferes with nucleic acid synthesis and prevents the formation of RNA and DNA.
Dosage
Crohn's disease:
- Adult: Initially 1-1.5 mg/kg daily, may increase to 125 mg daily.
- Child: Initially 1-1.5 mg/kg daily increased to a max of 75 mg daily
- Adult: Usual maintenance dose: Initially, 1.5-2.5 mg/kg daily as a single dose, usually used in combination with methotrexate. Dose may vary individually based on response and tolerance. Monitor blood counts at least once wkly. Withdraw treatment immedietely if there is a sharp drop in the white cell count or severe bone-marrow depression. May resume treatment slowly and carefully if white cell count remains constant for 2-3 days or rises. Reduce dose when used with allopurinol.
- Child: Usual maintenance dose: Initially, 1.5-2.5 mg/kg daily as a single dose, usually used in combination with methotrexate. Dose may vary individually based on response and tolerance. Monitor blood counts at least once wkly. Withdraw treatment immedietely if there is a sharp drop in the white cell count or severe bone-marrow depression. May resume treatment slowly and carefully if white cell count remains constant for 2-3 days or rises. Reduce dose when used with allopurinol.
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Administration
Should be taken on an empty stomach. Best taken on an empty stomach 1 hr before or 2 hr after meals. Ensure adequate fluid intake.
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Interaction
Anticoagulant action of warfarin may be inhibited by mercaptopurine. Enhanced toxicity with myelosuppressive drugs.
Contraindications
Pregnancy and lactation. Prior resistance to mercaptopurine or thioguanine; severe liver disease; severe bone marrow suppression.
Side Effects
Hyperuricaemia, bone marrow toxicity, hypoplasia, anorexia, diarrhoea, leukopenia, thrombocytopenia, intestinal ulceration, crystalluria with haematuria, immunosuppression, interstitial pneumonitis. Cutaneous hyperpigmentation, alopecia.
Pregnancy & Lactation
Pregnancy category D. There is positive evidence of human foetal risk, but the benefits from use in pregnant women may be acceptable despite the risk (e.g., if the drug is needed in a life-threatening situation or for a serious disease for which safer drugs cannot be used or are ineffective).
Precautions & Warnings
Hepatic or renal dysfunction; monitor hepatic function periodically. Mercaptopurine is potentially carcinogenic. Thiopurine S-methyl transferase (TPMT) deficiency; porphyria.
Use in Special Populations
Renal Impairment: Dosage may need to be reduced.
Hepatic Impairment:
For patients with homozygous TPMT deficiency: Substantial reduction is required.
For patients with heterozygous TPMT deficiency: Some may require reduction but most will tolerate the usual dosages.
Hepatic Impairment:
- Crohn's disease: Dosage may need to be reduced.
- Acute lymphocytic leukemia: Dosage may need to be reduced
For patients with homozygous TPMT deficiency: Substantial reduction is required.
For patients with heterozygous TPMT deficiency: Some may require reduction but most will tolerate the usual dosages.
Therapeutic Class
Cytotoxic Chemotherapy
Storage Conditions
Store at 20-25° C
