Mercaptopurine
Also known as: Purinethol, Flocofil, Ismipur, Mercap, Mercaptina, Puri-Nethol, Varimer
- **Safe Handling**: This is a potent immunosuppressive and anti-cancer drug. Wash your hands thoroughly after administering the tablets. Pregnant women or immunocompromised individuals should avoid handling this medication. - **Watch for Toxicity**: Contact your veterinarian immediately if your pet exhibits signs of abnormal bleeding, bruising, loss of appetite, vomiting, diarrhea, or signs of infection (such as fever or extreme lethargy). - **Strict Monitoring**: Your pet will require frequent blood tests to ensure the drug is not damaging their bone marrow or liver. Do not skip these appointments. - **Long-term Risks**: Be aware that long-term use of immunosuppressants carries a risk of severe toxicity, including an increased susceptibility to infections or the development of secondary cancers.
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
What it is used for
- As an immunosuppressant in combination with corticosteroids for treating bullous pemphigoid
- For erosive, immune-mediated polyarthritis in combination with corticosteroids
- For treatment of immune-mediated diseases or acute lymphocytic and granulocytic leukemias
How it is given
Possible side effects
- Nausea
- Anorexia
- Vomiting
- Diarrhea
- Bone marrow suppression (leukopenia, thrombocytopenia, anemia)
- Hepatotoxicity
- Pancreatitis
- Gastrointestinal ulceration (including oral ulcers)
- Dermatologic reactions
Cautions & contraindications
- Hypersensitivity to mercaptopurine
- Pregnancy (teratogenic and mutagenic)
- > **Risk vs. Benefit Warning**: Use with extreme caution in patients with pre-existing hepatic dysfunction, bone marrow depression, active infections, renal function impairment (dosage adjustment required), or a history of urate urinary stones. * **Teratogenicity**: Mercaptopurine is mutagenic and teratogenic (FDA Category D). Do not use in pregnant animals unless the benefit strictly outweighs the risk. * **Nursing**: Unknown if excreted in milk; use milk replacer for nursing bitches or queens. * **Laboratory Interference**: May cause falsely elevated serum glucose and uric acid values on SMA 12/60 analyzers.
Drug interactions
- Allopurinol: Decreases hepatic metabolism of mercaptopurine via xanthine oxidase inhibition. Dose of mercaptopurine must be drastically reduced (to 1/4-1/3 of usual dose) if used concurrently.
- Aminosalicylates (mesalamine, sulfasalazine): May increase the risk for mercaptopurine toxicity.
- Hepatotoxic drugs (halothane, ketoconazole, valproic acid, phenobarbital, primidone, doxorubicin): Increased risk of hepatotoxicity; use cautiously together.
- Immunosuppressive drugs (azathioprine, cyclophosphamide, corticosteroids): Increased risk of severe infection due to additive immunosuppression.
- Myelosuppressive drugs (antineoplastics, chloramphenicol, flucytosine, amphotericin B, colchicine, trimethoprim/sulfa): Additive bone marrow depression; use with extreme caution.
- Vaccines, live: Increased risk of vaccine-induced infection; use with caution or avoid during therapy.
- Warfarin: Mercaptopurine may reduce the anticoagulant effect of warfarin.
Frequently asked questions
What is Mercaptopurine used for in pets?
- **Safe Handling**: This is a potent immunosuppressive and anti-cancer drug. Wash your hands thoroughly after administering the tablets. Pregnant women or immunocompromised individuals should avoid handling this medication. - **Watch for Toxicity**: Contact your veterinarian immediately if your pet exhibits signs of abnormal bleeding, bruising, loss of appetite, vomiting, diarrhea, or signs of infection (such as fever or extreme lethargy). - **Strict Monitoring**: Your pet will require frequent blood tests to ensure the drug is not damaging their bone marrow or liver. Do not skip these appointments. - **Long-term Risks**: Be aware that long-term use of immunosuppressants carries a risk of severe toxicity, including an increased susceptibility to infections or the development of secondary cancers.
Is Mercaptopurine safe for my pet?
Dosage must be set by your veterinarian for your specific pet. Never give human medication or another pet’s prescription without veterinary guidance.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
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