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Lomustine for Dogs and Cats

By Barbara Forney, VMD

Last reviewed: 9/20/2022

Commonly prescribed for: Rescue Protocols for Relapsed Canine Lymphoma; Cutaneous Lymphoma of Dogs; Relapsing Lymphosarcoma in Cats

Species: Dogs and Cats

Therapeutic Class: Chemotherapeutic Alkylating Agent.


Basic Information

Lomustine is a chemotherapeutic alkylating agent. It also commonly is referred to as CCNU. Alkylating agents disrupt DNA transcription and RNA replication. They are not cell-stage specific. Lomustine is metabolized in the liver and excreted in the kidneys. It is highly lipid-soluble and crosses the blood-brain barrier into the CNS. Lomustine is absorbed rapidly from the GI tract. In order to decrease nausea, lomustine should be given on an empty stomach. There is some topical absorption of lomustine.

Dogs and Cats

Lomustine is used commonly and considered efficacious in rescue protocols for relapsed canine lymphoma. Numbers regarding remission vary but complete or partial remission may be achieved in as many as 25% - 50% of dogs with drug-resistant lymphoma. Results with the use of lomustine as a first-line treatment for canine lymphoma are less promising, although it may be used as a first-line treatment when finances and or owner compliance limit the treatment options. Lomustine also is used in relapsing lymphosarcoma in cats.

Lomustine is used as a first-line drug to treat cutaneous lymphoma of dogs with a response rate of 80 - 90% and 26% achieving complete remission. The duration of treatment to response is reported to be about three to four months.

Lomustine is helpful for chemotherapy of mast cell tumors in both dogs and cats. Complete surgical removal is the most-effective treatment for canine mast cell tumors; multiple authors emphasize the importance of clean margins. In tumors that are not completely resectable due to location or size, radiation and chemotherapy have both proved useful. Chemotherapy usually is used in tumors that are grade II or above. Lomustine is safe to use with prednisone and has provided complete or partial remission in a number of cases. One study gave the overall response rate in cats with mast cell tumors as 50%. Lomustine was found not to be beneficial in dogs with advanced mast cell tumors that had bone marrow involvement.

The most-common primary intracranial tumor of dogs is astrocytoma (glial cell tumor). Because active metabolites of lomustine are found in the CSF it has been used in the palliative treatment of intracranial tumors. There also is a favorable report of the use of lomustine within a multiple-drug protocol to treat optic neuritis secondary to granulomatous meningoencephalomyelitis.

Lomustine Side Effects

Side effects include bone-marrow suppression, including anemia, thrombocytopenia, and leucopenia. Approximately 40% of treated dogs will have neutrophil counts of <1,000 cells/uL at seven days after treatment. GI effects can include vomiting, anorexia, and diarrhea. Hepatotoxicosis, alopecia, corneal de-epithelization, and renal and pulmonary damage also may be experienced.

Precautions

  • Animals with anemia, bone-marrow depression, decreased pulmonary function, infection, and decreased liver and kidney function should receive lomustine only when the benefits outweigh the potential risks.
  • The occurrence of neutropenia is a dose-limiting factor for lomustine. The nadir for thrombocytopenia and neutropenia usually is at seven to ten days post therapy. Hematologic changes may be delayed and cumulative, although more commonly they are resolved before the next treatment. Platelet counts should be performed before each treatment.
  • Lomustine can cause chronic irreversible liver failure in dogs. Liver enzymes should be evaluated prior to each treatment. Manifestation of hepatotoxicity may be delayed by as long as four weeks after cessation of treatment. Hepatotoxicity has not been reported in cats.
  • Because Lomustine is excreted by the kidneys, dose modification may be needed in animals with pre-existing renal disease. Glucosuria may be an early sign of renal tubular damage.

Drug Interactions

  • Lomustine should be used with caution with other myelosuppressive or immunosuppressive drugs due to additive bone-marrow suppression or increased risk of infection.
  • Vaccination with live virus vaccines should be avoided in animals receiving lomustine.

Overdose

Lomustine has a narrow effective-dose range prior to toxicity. Overdose should be treated aggressively with gut-emptying protocols.
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