Drug Index


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 :

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.

Renal Dose :

Dose in Renal Impairment GFR (mL/min)
20-50Caution – reduce dose.
10-20Caution – reduce dose.
<10Caution – reduce dose.

Dose in Patients undergoing Renal Replacement Therapies
CAPDUnknown dialysability. Dose as in GFR<10 mL/min
HDDialysed. Dose as in GFR<10 mL/ min
HDF/High fluxDialysed. Dose as in GFR<10 mL/ min
CAV/VVHDUnknown dialysability. Dose as in GFR=10–20 mL/min

Hepatic Dose :

Start at the low end of the dosing range in patients with hepatic impairment.
03/20/2024 23:56:42 Mercaptopurine
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