Mercaptopurine Accord (Mercaptopurine Monohydrate)

Mercaptopurine is used in hematologic malignancies and certain inflammatory conditions where it interferes with purine synthesis.

• Acute lymphoblastic leukemia (ALL): helps achieve remission by inhibiting proliferation of leukemic lymphoblasts.
• Chronic myeloid leukemia (CML): contributes to disease control by suppressing abnormal myeloid cell growth.
• Inflammatory bowel disease (IBD): reduces intestinal inflammation and maintains remission in ulcerative colitis or Crohn's disease.

• Mercaptopurine is a purine analog that is metabolized intracellularly to thio‑inosine monophosphate, which inhibits de novo purine synthesis and is incorporated into DNA and RNA. This incorporation disrupts nucleic acid synthesis, leading to cytotoxicity in rapidly dividing cells and induces immunosuppression by affecting lymphocyte proliferation. The drug also interferes with the salvage pathway, further limiting nucleotide availability and enhancing its antimetabolic effect.

Mercaptopurine may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Nausea: transient stomach upset that may improve with food.
• Vomiting: occasional episodes, often manageable with anti‑emetics.
• Loss of appetite: reduced desire to eat, potentially leading to weight loss.
• Mild leukopenia: slight decrease in white blood cells, monitored by regular blood tests.

Serious or Rare Side Effects

• Severe bone marrow suppression: profound pancytopenia requiring medical intervention.
• Hepatotoxicity: elevated liver enzymes or liver injury, necessitating liver function monitoring.
• Pancreatitis: inflammation of the pancreas presenting with abdominal pain and elevated enzymes.

When prescribing Mercaptopurine, clinicians should observe several safety measures.

• Dose adjustment: monitor complete blood counts regularly and modify dose as needed.
• Hepatic function: assess liver enzymes before initiation and during therapy.
• Renal function: evaluate kidney function for appropriate dosing considerations.
• Infection risk: avoid live vaccines and watch for signs of infection.
• TPMT activity: test thiopurine methyltransferase levels prior to starting treatment.
• Store at ambient temperature below 25°C: keep in the original container, protect from moisture and direct sunlight.

Mercaptopurine interacts with several medicines; awareness helps prevent toxicity.

Major Interactions (Avoid)

• Allopurinol: may increase mercaptopurine toxicity; dose reduction is required.
• Azathioprine: additive myelosuppression; concurrent use is generally avoided.
• Warfarin: may enhance anticoagulant effect; INR should be closely monitored.

Moderate Interactions (Monitor Closely)

• 5‑Fluorouracil: potential additive bone marrow suppression.
• Cyclophosphamide: may increase risk of cytopenias.
• Rituximab: possible enhanced immunosuppression.