Drug Index

Mercaptopurine

 
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Mechanism :

Mercaptopurine competes with hypoxanthine and guanine for the enzyme hypoxanthine-guanine phosphoribosyl transferase (HGPRTase) and is itself converted to thioinosinic acid (TIMP). This intracellular nucleotide inhibits several reactions involving inosinic acid (IMP). In addition, 6-methylthioinosinate (MTIMP) is formed by the methylation of TIMP. Both TIMP and MTIMP have been reported to inhibit glutamine-5-phosphoribosylpyrophosphate amidotransferase, the first enzyme unique to the de novo pathway for purine ribonucleotide synthesis.


Indication :

• Acute lymphoblastic leukemia

• Lymphoma

• Non-Hodgkin Lymphoma (NHL)

• Crohn’s disease - steroid dependent/intractable

• Acute myeloid Leukemia

• Ulcerative colitis

• Histiocytosis


Contraindications :

Should not be used unless a diagnosis of acute lymphatic leukemia has been adequately established. Contraindicated in patients whose disease has demonstrated prior resistance to this drug and in patients who have a hypersensitivity to mercaptopurine or any component of the formulation. There is usually complete cross-resistance between mercaptopurine and thioguanine.


Dosing :

Leukemia/lymphoma/NHL:

Induction: 2.5-5 mg/kg once daily orally. Maintenance: 1.5-2.5 mg/kg/day.

Crohn’s disease:

Above 2 years: 1-1.5 mg/kg once at night, Max dose: 75 mg/day.


Adverse Effect :

Myelosuppression, anemia, leukopenia, and thrombocytopenia, hyperuricemia and hyperuricosuria, nausea, vomiting, stomatitis, diarrhea, ulcer formation. Miscellaneous: skin rashes, alopecia and hyperpigmentation.


Interaction :

Allopurinol: Delayed catabolism of mercaptopurine and the strong likelihood of inducing severe toxicity.
Thioguanine: Usually complete cross-resistance between mercaptopurine and thioguanine.
trimethoprim-sulfamethoxazole: Enhanced marrow suppression has been noted in some patients also receiving trimethoprim-sulfamethoxazole.
Warfarin: Inhibition of the anticoagulant effect of warfarin, when given with mercaptopurine, has been reported.


07/17/2019 20:41:17 Mercaptopurine
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