Generic Name

Mercaptopurine

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Classification

FDA Approved Indications

• Acute lymphoblastic leukemia (ALL) in combination with other chemotherapeutic agents

Mechanism of Action

Mercaptopurine inhibits purine nucleotide biosynthesis by integrating into DNA and RNA, leading to the disruption of cell proliferation and inducing apoptosis in rapidly dividing cells.

Dosage and Administration

Adult: Initial dose: 1-4 mg/kg orally once daily, adjusted based on response and tolerability.

Pediatric: Dose based on body surface area, typically 50-75 mg/m² orally once daily, adjusted according to toxicity and therapeutic response.

Geriatric: Use with caution; start at lower end of dosing range due to increased risk of toxicity.

Renal Impairment: Adjust dose based on degree of impairment; consult renal function guidelines.

Hepatic Impairment: Use cautiously; hepatic function should be monitored, dosage modifications may be necessary.

Pharmacokinetics

Absorption: Well absorbed orally.

Distribution: Widely distributed, crosses blood-brain barrier.

Metabolism: Primarily metabolized hepatically by xanthine oxidase to inactive metabolites; also metabolized by thiopurine methyltransferase.

Excretion: Excreted mainly in urine.

Half Life: Approximately 5 hours, but may be longer in cases of impaired metabolism.

Contraindications

• Hypersensitivity to mercaptopurine.
• Active infections.

Precautions

• Leukopenia, anemia, thrombocytopenia—monitor blood counts regularly.
• Use cautiously in patients with hepatic or renal impairment.
• Potential for myelosuppression—monitor CBC closely.
• Pregnancy category D; fetal toxicity risk—use only if clearly necessary and benefits outweigh risk.

Adverse Reactions - Common

• Bone marrow suppression (neutropenia, anemia, thrombocytopenia) (Common)
• Nausea, vomiting (Common)
• Hepatotoxicity (Uncommon)

Adverse Reactions - Serious

• Severe myelosuppression leading to infection or bleeding (Serious)
• Liver failure or hepatotoxicity (Serious)
• Secondary malignancies (rare) (Rare)

Drug-Drug Interactions

• Allopurinol (increases mercaptopurine levels, risk of toxicity),
• Immunosuppressants

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Patient/Family Teaching

• Report signs of infection, unusual bleeding, or bruising immediately.
• Avoid live vaccines during therapy.
• Maintain adequate hydration.
• Follow scheduled blood tests and follow-up appointments.

Special Considerations

Black Box Warnings:

• Myelosuppression leading to infection, bleeding, and anemia; potential secondary malignancies.

Genetic Factors: Thiopurine methyltransferase (TPMT) activity affects drug metabolism; testing recommended before therapy to adjust dosing.

Lab Test Interference: May cause false-positive urine ketone tests.

Overdose Management

Signs/Symptoms: Severe bone marrow suppression, infection, bleeding, hepatic toxicity.

Treatment: Supportive care including transfusions, antibiotics, and hematopoietic growth factors as needed; no specific antidote.

Storage and Handling

Storage: Store at room temperature, away from moisture and light.

Stability: Stable under recommended storage conditions.