• Therapeutic Class: Immunosuppressant, Alkylating Agent
  • Common Uses: Chlorambucil is primarily used to treat a variety of immune-mediated disorders and cancers, including lymphoma and leukemia, across multiple species such as dogs, cats, and occasionally horses.
  • Species: Dogs, Cats, Horses

Basic Information:

  • Mechanism of Action: Chlorambucil functions as an alkylating agent that disrupts DNA replication and RNA transcription by forming covalent bonds with nucleic acids. This activity suppresses both the immune system and abnormal cell growth, making it effective against cancers and autoimmune diseases.
  • Absorption and Metabolism: It is well-absorbed orally and metabolized in the liver, necessitating careful monitoring in animals with liver impairments.

Veterinary Medicine Uses:

  • Dogs: Used to treat conditions such as lymphoma, chronic lymphocytic leukemia, and immune-mediated skin disorders. Often combined with corticosteroids like prednisone to enhance efficacy and reduce side effects.
  • Cats: Effective for managing lymphocytic leukemia, inflammatory bowel disease, and certain dermatological conditions. Preferred over azathioprine in feline patients due to better tolerance.
  • Horses: Part of multidrug protocols to address lymphoma, although less commonly used than in smaller pets.

Potential Side Effects:

  • Gastrointestinal: Vomiting, diarrhea, and appetite loss are common.
  • Hematologic: Bone marrow suppression may manifest as anemia, leukopenia, or thrombocytopenia.
  • Neurological: Rare but serious side effects include seizures, especially at high doses or in cases of overdose.
  • Dermatological: Hair loss and delayed regrowth can occur, particularly noted in certain dog breeds.


  • Handling: Gloves should be worn when administering the drug due to its cytotoxic nature.
  • Contraindications: Not recommended for use in pregnant or lactating animals, or in those with severe liver or bone marrow diseases.
  • Monitoring: Regular blood work is required to monitor liver function and blood cell counts, adjusting dosage as necessary to avoid toxicity.

Drug Interactions:

  • Increased Risk with Other Agents: Use with caution when combined with other immunosuppressants, myelosuppressive drugs, or certain antibiotics due to potential for heightened toxicity.

Dosage and Administration:

  • Individualized Regimen: Dosage and frequency depend on the specific condition being treated and the individual response of the animal. Typically administered orally.
  • Safety Measures: Pet owners should avoid direct contact with the pet’s bodily fluids for 48 hours post-administration.

Overdose Management:

  • Immediate veterinary intervention is crucial. Treatment may include gastric emptying, supportive care, and blood-component therapy depending on the severity of symptoms and blood work results.