Also found in: Dictionary, Thesaurus, Acronyms, Encyclopedia, Wikipedia.


a purine analogue in which sulfur replaces the oxygen atom of purine; it is used as an antineoplastic agent primarily for treatment of acute lymphoblastic leukemia. It is also used an immunosuppressant in the treatment of Crohn's disease and ulcerative colitis. Called also 6-mercaptopurine and 6-MP.

mercaptopurine (6-mercaptopurine, 6-MP)

Purinethol, Puri-Nethol (UK)

Pharmacologic class: Antimetabolite

Therapeutic class: Antineoplastic

Pregnancy risk category D

FDA Box Warning

• Don't give drug unless diagnosis of acute lymphatic leukemia is confirmed and responsible physician knows how to assess response to chemotherapy.


Inhibits DNA and RNA synthesis, suppressing growth of certain cancer cells


Tablets: 50 mg

Indications and dosages

Maintenance therapy for acute lymphatic (lymphocytic, lymphoblastic) leukemia

Adults and children: On complete hematologic remission, 1.5 to 2.5 mg/kg/day P.O. as a single dose (combined with other agents as prescribed).


• Hypersensitivity to drug or its components

• Prior resistance to drug or thioguanine

• Breastfeeding


Use cautiously in:

• renal or hepatic impairment

• decreased platelet or neutrophil counts after chemotherapy or radiation

• inherited thiopurine methyltransferase deficiency

• pregnant patients.


• Follow facility protocols regarding proper handling and disposal of drug.

Don't handle drug if you are pregnant.

• Be aware that total daily dosage is calculated to nearest multiple of 25 mg and given once daily.

Be aware that when mercaptopurine is given with allopurinol, mercaptopurine dosage must be reduced to one-third to one-fourth of usual dosage to avoid severe toxicity.

Withdraw drug immediately if white blood cell (WBC) or platelet count falls rapidly or steeply.

Adverse reactions

GI: nausea, vomiting, anorexia, diarrhea, GI ulcers, painful oral ulcers, pancreatitis

Hematologic: anemia, leukopenia, thrombocytopenia

Hepatic: jaundice, hepatotoxicity

Metabolic: hyperuricemia

Skin: rash, hyperpigmentation


Drug-drug. Allopurinol (more than 300 mg), aminosalicylate derivatives (mesalazine, olsalazine, sulfasalazine): increased bone marrow depression

Warfarin: decreased anticoagulant effect

Drug-diagnostic tests. Hemoglobin, platelets, red blood cells, uric acid, WBCs: increased values

Patient monitoring

Watch for signs and symptoms of hepatotoxicity.

• Monitor weekly CBC with white cell differential and platelet count.

• Assess bone marrow aspiration and biopsy results, as necessary, to aid assessment of disease progression, resistance to therapy, and drug-induced marrow hypoplasia.

• Monitor serum uric acid level.

• Evaluate fluid intake and output.

• Monitor liver function tests and bilirubin level weekly at start of therapy, then monthly.

Patient teaching

Instruct patient to immediately report fever, sore throat, increased bleeding or bruising, or signs or symptoms of liver problems (right-sided abdominal pain, yellowing of skin or eyes, nausea, vomiting, clay-colored stools, or dark urine).

• Advise both male and female patients to use reliable contraception.

• Encourage patient to maintain adequate fluid intake.

• Caution patient not to get vaccinations without consulting prescriber.

• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.


/mer·cap·to·pur·ine/ (6-MP) (mer-kap″to-pūr´ēn) a sulfur-containing purine analogue, used as an antineoplastic and as an immunosuppressant.


A purine analog, C5H4N4S, that interferes with the synthesis of purines and is used primarily in the treatment of certain forms of leukemia.


an antineoplastic and immunosuppressive; a purine antimetabolite. Also called 6-mercaptopurine (6-MP).
indications It is prescribed in the treatment of malignant neoplastic diseases, especially as maintenance therapy for acute lymphocytic leukemia.
contraindication Known hypersensitivity to this drug prohibits its use.
adverse effects Among the more severe adverse effects are bone marrow depression and acute GI disturbances, including nausea, vomiting, diarrhea, and stomatitis.


An antimetabolic chemotherapeutic structural analogue (thiol replaces 6-hydroxyl) of hypoxanthine, which is activated by hypoxanthine phosphoribosyl transferase and converted in vivo to thioinosinic acid, a competitive inhibitor in purine synthesis that targets rapidly dividing cells (e.g., in ALL, AML). The wide variation in 6-MP bioavailability and suboptimal doses during maintenance regimens are attributable causes for the high incidence of relapse in children with ALL in remission.

Adverse effects
Myelosuppression, anorexia, nausea, vomiting, jaundice.


A CYTOTOXIC drug used in combination with others in the treatment of acute LEUKAEMIA. The drug is on the WHO official list. A brand name is Puri-Nethol.

mercaptopurine, 6-mercaptopurine

an antimetabolite that acts by blocking purine synthesis; used as an antineoplastic agent, primarily in the treatment of leukemia and lymphosarcoma.
References in periodicals archive ?
Genetic variation in response to 6 mercaptopurine for childhood acute lymphoblastic leukemia.
Molecular diagnosis of thiopurine S-methyltransferase deficiency: genetic basis for azathioprine and mercaptopurine intolerance.
Mercaptopurine therapy intolerance and heterozygosity at the thiopurine S-methyltransferase gene locus.
HPLC determination of thiopurine nucleosides and nucleotides in vivo in lymphoblasts following mercaptopurine therapy.
Methylation of mercaptopurine, thioguanine, and their nucleotide metabolites by heterologously expressed human thiopurine S-methyltransferase.
Variable mercaptopurine metabolism and treatment outcome in childhood lymphoblastic leukemia.
Systemic exposure to mercaptopurine as a prognostic factor in acute lymphocytic leukemia in children.
Application of pharmacogenetics to optimization of mercaptopurine dosing.
Patient TPMT TPMT Withdrawal of azathioprine/ genotype activity (a) mercaptopurine because of side effects 162-9 * 1/* 3A 16 Yes 162-58 * 1/* 3A 18 No 150-3 * 1/* 3A 14 Yes 149-9 * 1/* 3A 33 No 149-16 * 1/* 3A 19 Yes 149-40 * 1/* 3A 21 No 140-45 * 1/* 3A 21 Yes 140-49 * 1/* 3A 23 No 140-90 * 1/* 3A 31 No 150-6 * 1S/* 3A 11 Yes 140-105 * 1S/* 3A 14 Yes 149-31 * 1/* 3C 22 Yes 140-15 * 1/* 3D 22 Yes (a) TPMT enzyme activity was measured by HPLC method.
Lifelong maintenance therapy of UC with aminosalicylates, azathioprine, or mercaptopurine to reduce the risk of relapse is usually recommended.
Azathioprine or mercaptopurine may be useful as secondary agents and to allow steroid reduction; but their onset of action is too slow to recommend these agents as first line therapy of active CD.