Mercaptopurine

Trade Names:
Purinethol
- Tablets 50 mg

Pharmacology

User Reviews & Ratings As a treatment for... Avg User Ratings [?] Crohn's Disease, Maintenance 0 reviews Rate it! 9.5 Ulcerative Colitis, Maintenance 0 reviews Rate it! 8.0 Inflammatory Bowel Disease Be the first to rate it 0 reviews Showing 3 of 6 conditions - Show All... Compare with other drugs.

Mercaptopurine competes with hypoxanthine and guanine for the enzyme hypoxanthine-guanine phosphoribosyltransferase and is 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 inhibit de novo purine ribonucleotide synthesis.

Pharmacokinetics

Absorption

Mercaptopurine absorption is incomplete and variable; averaging 50%.

Distribution

Protein binding is approximately 19% (over concentration of 10 to 50 mcg/mL). Entry into CSF is negligible.

Metabolism

The major pathways for metabolism are hepatic via methylation and oxidation.

Elimination

Approximately 50% is excreted in urine within 24 h as parent drug and metabolites. Plasma t _½ is 47 minutes in adults.

Special Populations

Plasma t _½ is 21 minutes.

Indications and Usage

For maintenance therapy of acute lymphatic (lymphocytic, lymphoblastic) leukemia.

Contraindications

Prior resistance to this drug; hypersensitivity to the drug or any component of this formulation.

Dosage and Administration

PO Usual range is 1.5 to 2.5 mg/kg/day as a single dose.

PO Superior results have been obtained when mercaptopurine has been combined with other agents, most frequently methotrexate, for remission maintenance. Mercaptopurine should rarely be relied upon as a single agent for maintenance of remissions induced in acute leukemia.

When allopurinol and mercaptopurine are administered concomitantly, the dose of mercaptopurine must be reduced to 1/ 3 to 1/ 4 of the usual dose.

Storage/Stability

Store tablets at controlled room temperature (59° to 77°F). Protect from moisture.

Drug Interactions

Inhibition of mercaptopurine metabolism; coadministration may cause increased toxicity. Reduce dose of mercaptopurine to 1/ 3 to 1/ 4 of the usual dose.

Potentiates bone marrow suppression associated with mercaptopurine.

May increase oral bioavailability of mercaptopurine.

Mercaptopurine may decrease the hypoprothrombinemic effect of warfarin; monitor and adjust warfarin therapy as necessary.

Laboratory Test Interactions

None well documented.

Adverse Reactions

Dermatologic

Alopecia; hyperpigmentation; rash.

GI

Anorexia; intestinal ulceration; mild diarrhea; nausea; oral lesions resembling thrush; sprue-like symptoms; vomiting.

Genitourinary

Hyperuricemia; hyperuricosuria; oligospermia.

Hematologic

Bone marrow suppression; bone marrow toxicity; marrow hypoplasias.

Precautions

Pregnancy

Category D .

Lactation

Undetermined.

Elderly

Use with caution because of the greater frequency of decreased hepatic, renal, or cardiac function, and concomitant diseases or other drug therapy. Start at the low end of the dosing range.

Renal Function

Start with smaller doses because of the possibility of slower drug elimination and a greater cumulative effect in patients with renal function impairment.

Hepatic Function

Start with smaller doses because of the possibility of slower drug elimination and a greater cumulative effect in patients with hepatic function impairment.

Bone marrow toxicity

Most consistent dose-related toxicity is bone marrow suppression manifested by anemia, leukopenia, or thrombocytopenia.

Enzyme deficiency

There are patients with inherent deficiency of the enzyme thiopurine methyltransferase who may be unusually sensitive to the myelosuppressive effects of mercaptopurine and prone to developing rapid bone marrow suppression.

Hepatotoxicity

Hepatotoxicity occurs with greatest frequency when doses of 2.5 mg/kg/day are exceeded. Deaths have occurred from hepatic necrosis.

Immunosuppression

Induction of immunity to infectious agents or vaccines will be subnormal in patients receiving mercaptopurine. Carefully consider effect with regard to intercurrent infections and risk of subsequent neoplasm.

Overdosage

Symptoms

Anorexia, nausea, vomiting, diarrhea, myelosuppression, liver dysfunction, gastroenteritis.

Patient Information

• Advise patient, family, or caregiver that medication may be used in combination with other agents to achieve max benefit possible.
• Advise patient to take as a single daily dose.
• Advise patient, family, or caregiver to immediately report any of the following to health care provider: rash; hives; difficulty breathing; fever, chills, or other signs of infection; bleeding or unusual bruising; sores in mouth; dark urine; yellowing of skin or eyes.
• Advise patient, family, or caregiver to report any of the following to health care provider: persistent nausea, vomiting, diarrhea, or appetite loss; persistent or worsening general body weakness.
• Advise women of childbearing potential to avoid becoming pregnant during therapy.

Link to Page

Print Page

Email Page

Add to List