Mercaptopurine is indicated for maintenance therapy of acute lymphatic (lymphocytic, lymphoblastic) leukemia as part of a combination regimen. The response to this medicine depends on the specific subclassification of acute lymphatic leukemia and on whether the patient is pediatric or adult.

Mercaptopurine is not effective for the prophylaxis or treatment of central nervous system leukemia. It is also not effective in acute myelogenous leukemia, chronic lymphatic leukemia, lymphomas (including Hodgkin’s disease), or solid tumors.

Mercaptopurine is a purine antagonist that is converted inside the cell into active nucleotides, including thioinosinic acid. These nucleotides inhibit several biochemical reactions, which ultimately interfere with nucleic acid synthesis and prevent the formation of RNA and DNA.

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

Acute lymphocytic leukemia:

• 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. 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.

The anticoagulant effect of warfarin may be reduced by mercaptopurine. Toxicity may increase when it is used together with myelosuppressive drugs.

Mercaptopurine is contraindicated during pregnancy and lactation. It is also contraindicated in patients with prior resistance to mercaptopurine or thioguanine, severe liver disease, or severe bone marrow suppression.

Possible side effects include hyperuricaemia, bone marrow toxicity, hypoplasia, anorexia, diarrhea, leukopenia, thrombocytopenia, intestinal ulceration, crystalluria with haematuria, immunosuppression, interstitial pneumonitis, cutaneous hyperpigmentation, and alopecia.

Mercaptopurine is classified as pregnancy category D. There is evidence of human fetal risk, but in certain serious or life-threatening conditions, the potential benefit may justify use despite the risk when safer alternatives are not suitable or effective.

Use mercaptopurine cautiously in patients with hepatic or renal dysfunction, and monitor liver function periodically. Mercaptopurine is considered potentially carcinogenic. Extra caution is also needed in patients with thiopurine S-methyl transferase (TPMT) deficiency and in those with porphyria.

Renal Impairment: Dosage adjustment may be necessary, and dose reduction should be considered.

Hepatic Impairment:

• Crohn's disease: Dose reduction may be required.
• Acute lymphocytic leukemia: Dose reduction may be required.

Dosage should be adjusted in patients with thiopurine-S-methyltransferase (TPMT) deficiency to reduce the risk of severe myelotoxicity.

For patients with homozygous TPMT deficiency: A significant dose reduction is required.

For patients with heterozygous TPMT deficiency: Some patients may need dose reduction, although most can tolerate standard doses.

Cytotoxic Chemotherapy.

Store at 20-25°C.