MERCAPTOPURINE (6-MP, 6-MERCAPTOPURINE)

(mer-kap-toe-pyoor'een)

Purinethol
Classifications: antineoplastic; antimetabolite, purine antagonist; immunosuppressant;
Therapeutic: antineoplastic; immunosuppressant
Pregnancy Category: D

Availability

50 mg tablets

Action

Antimetabolite and purine antagonist. Inhibits purine metabolism. 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.

Therapeutic Effect

Delayed immunosuppressive properties and carcinogenic potential.

Uses

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.

Unlabeled Uses

Prevention of transplant graft rejection; SLE; rheumatoid arthritis; Crohn's disease.

Contraindications

Prior resistance to mercaptopurine; first trimester of pregnancy (category D); lactation; infections.

Cautious Use

Impaired kidney or liver function; concomitant use with allopurinol.

Route & Dosage

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

Administration

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.

Adverse Effects (≥1%)

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.

Interactions

Drug: Allopurinol may inhibit metabolism and thus increase toxicity of mercaptopurine; may potentiate or antagonize anticoagulant effects of warfarin.

Pharmacokinetics

Absorption: Approximately 50% absorbed from GI tract. Peak: 2 h. Distribution: Distributes into total body water. Metabolism: Rapidly by xanthine oxidase in liver. Elimination: 11% in urine within 6 h. Half-Life: 20–50 min.

Nursing Implications

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.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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