Mercaptopurine (Dosage)

Mercaptopurine is an immunosupressant and antineoplastic agent used in combination with other drugs to treat acute lymphoblastic leukemia. The most adverse effect of the treatment with mercaptopurine is bone marrow suppression.

ACTION MECHANISM:

Mercaptopurine is an antineoplastic non-nucleoside antimetabolite of the purine bases.

It acts as a false substrate in the synthesis process (S phase of the cell cycle) mimicking the essential constituents of the nucleic acids, causing the synthesis of an anomalous DNA or even the stop of the process of synthesis of the nucleic acids.

CONTRAINDICATIONS

Hypersensibility reactions to mercaptopurine.

Concomitancy with the yellow fever vaccine.

PRECAUTIONS:

Risk of immunosuppression, liver toxicity (weekly monitoring of liver function is recommended), renal toxicity (monitor uric acid levels in the blood and urine for possible hyperuricemia and hyperuricosuria, with risk of uric acid nephropathy).

Risk of myelosuppression, monitor hematologic parameters during treatment (it may be necessary to decrease doses of mercaptopurine when combined with substances that associate with myelosuppression)

Patients with hereditary deficiency of the enzyme thiopurine methyltransferase (TPMT) are more sensitive to the myelosuppressive effect of mercaptopurine and more likely to develop rapid marrow aplasia after initiation of treatment, which may be aggravated if given concomitantly with substances that inhibit TPMT (such as olsalazine, mesalazine, or sulfasalazine).

There are reports of a possible relationship between decreased TPMT activity and the presence of leukemias and secondary myelodysplasias in patients treated with 6-mercaptopurine in combination with other cytotoxic agents.

Mercaptopurine is a potential mutagenic and cancerigen drug.

SIDE EFFECTS:

Myelopathy: leucopenia/thrombocytopenia and anemia.

Anorexy, nausea, vomiting, stomatitis, biliary staging and hepatotoxicity.

PHARMACOLOGIC INTERACTIONS:

Mercaptopurine decreases the anticoagulant effect of warfarin or acenocoumarol

Decreases the efficacy of live vaccines.

Plasma concentrations of the drug are diminished with some foods such as milk and other dairy products.

Risk of severe myelosuppression in concomitancy with ribavirin.

Mercaptopurine AUC (area under the curve) is increased by methotrexate, adjust the dose of mercaptopurine to maintain an adequate white blood cell count.

BRAND NAME:

  • Mercaptopurine ®
  • Purinethol®
  • Purixan®

Gene or region studied

  • TPMT
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