MERCAPTOPURINE (6-MP, 6-MERCAPTOPURINE) 
(mer-kap-toe-pyoor'een)
Purinethol
Classifications: antineoplastic; antimetabolite, purine antagonist; immunosuppressant
Pregnancy Category: D
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50 mg tablets
Antimetabolite and purine antagonist. Inhibits purine metabolism by unclear mechanism. Blocks conversion of inosinic acid
to adenine and xanthine ribotides within sensitive tumor cells. Also inhibits adenine-containing coenzymes, suggesting an
influence over multiple cellular reactions.
Delayed immunosuppressive properties and carcinogenic potential.
Primarily for acute lymphocytic and myelogenous leukemia. Response in adults is less than in children, but mercaptopurine
is initial drug of choice. In chronic granulocytic leukemia, produces temporary remission.
Prevention of transplant graft rejection; SLE; rheumatoid arthritis; Crohn's disease.
Prior resistance to mercaptopurine; first trimester of pregnancy (category D); lactation; infections.
Impaired kidney or liver function; concomitant use with allopurinol.
Leukemias
Adult/Child: PO Loading Dose 2.5 mg/kg/d, may increase up to 5 mg/kg/d after 4 wk if needed PO Maintenance Dose 1.25–2.5 mg/kg/d
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Oral
- Give total daily dose at one time.
- Reduce dose of mercaptopurine usually by 1/3–1/4 when given concurrently with allopurinol.
- Store tablets in light- and air-resistant container.
GI: Stomatitis, esophagitis, anorexia, nausea, vomiting, diarrhea, intestinal ulcerations, impaired liver function, hepatic necrosis. Hematologic:
Leukopenia, anemia, eosinophilia, pancytopenia, thrombocytopenia, abnormal bleeding, bone marrow hypoplasia. Urogenital: Hyperuricemia, oliguria, renal impairment. Skin: Rash. Body as a Whole: Drug fever.
Drug:
Allopurinol may inhibit metabolism and thus increase toxicity of mercaptopurine; may potentiate or antagonize anticoagulant effects of
warfarin.
Absorption: Approximately 50% absorbed from GI tract. Peak: 2 h. Distribution: Distributes into total body water. Metabolism: Rapidly metabolized by xanthine oxidase in liver. Elimination: 11% excreted in urine within 6 h. Half-Life: 20–50 min.
Assessment & Drug Effects
- Lab tests: Monitor CBC with differential, platelet count, Hgb, Hct, and liver functions closely.
- Monitor for S&S of liver damage. Hepatic toxicity occurs most often when dose exceeds 2.5 mg/kg/d. Jaundice signals onset
of hepatic toxicity and may necessitate terminating use.
- Withhold drug and notify physician at the first sign of an abnormally large or rapid fall in platelet and leukocyte counts.
- Record baseline data related to I&O ratio and pattern and body weight.
- Check vital signs daily. Report febrile states promptly.
- Protect patient from exposure to trauma, infections, or other stresses (restrict visitors and personnel who have colds) during
periods of leukopenia.
- Report nausea, vomiting, or diarrhea. These may signal excessive dosage, especially in adults.
- Watch for signs of abnormal bleeding (ecchymoses, petechiae, melena, bleeding gums) if thrombocytopenia develops; report immediately.
Patient & Family Education
- Report any signs of bleeding (e.g., hematuria, bruising, bleeding gums).
- Report signs of hepatic toxicity (see Appendix F).
- Increase hydration (10–12 glasses of fluid daily) to reduce risk of hyperuricemia. Consult physician about desirable
volume.
- Notify physician of onset of chills, nausea, vomiting, flank or joint pain, swelling of legs or feet, or symptoms of anemia.
- Do not breast feed while using this drug.
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Canadian drug name;