Chlorambucil, commonly known as Leukeran®, is an immune system suppressant and also interferes with the growth and spread of cancer cells in the body. It is often prescribed for pets suffering from immune-mediated disorders or cancers such as leukemia and lymphoma.1 Since chlorambucil is an alkylating agent, it can form tight bonds with nucleic acids, disrupt DNA strands, and ultimately limit cell division. Normal cells undergo cell division as part of the cell cycle. Basically, the cell goes from the resting phase, through active growing phases, and then divides (mitosis). Alkylating agents such as chlorambucil are most effective during the resting phase and are cell cycle non-specific.2
Chlorambucil can also suppress antibody production and has antineoplastic properties which help to clear the body of abnormal cellular growths in blood and lymphatic systems. This medication is readily absorbed following oral administration and is metabolized by the liver. Most often, it is used in combination with other drugs such as prednisone.3
Chlorambucil is an immunosuppressant and anti-cancer medication used to treat canine cancers “off-label”. This latter term is used in veterinary medicine to refer to drugs that have been developed for humans but are modified for use in dogs. Be sure to review your veterinarian’s directions since they may differ from the labeling instructions accompanying the drug which are more applicable to human use. Canine cancers treated with chlorambucil include the following:
Chlorambucil is either prepared as a compounded liquid or in tablet form. Most often, the tablet is given with food and taken in orally.4 It is usually taken once daily, approximately 1 hour before or 2 hours after meals, for 3 to 6 weeks. Sometimes chlorambucil is taken intermittently as a single dose, once every 2 weeks, or as a single dose once a month.2,5. The length of treatment depends on the types of drugs your pet is taking, the type of cancer being treated, and your pet’s response to the drug.2 Your veterinarian may adjust the dose of chlorambucil depending on your pet’s response to treatment and to reduce the potential for adverse effects. The amount of chlorambucil your pet receives and how often it is administered depends on many factors, including height & weight, general health, other health problems, and the type of cancer or condition being treated. Chemotherapeutic drugs that affect cells only when they are dividing are called cell-cycle specific. Since chlorambucil affects cells when they are at rest, it is cell-cycle non-specific and is not typically given in cycles.2 Veterinarian will determine your dose and schedule.
Tell your veterinarian if your pet is allergic to chlorambucil, ingredients mixed with the chlorambucil, or reacts to other medications, vitamins or supplements. You can always ask your pharmacist for a list of “other ingredients” included in any medication. This is important since the product may contain inactive ingredients which can cause allergic reactions or other problems.
Also, be sure to mention if your dog is taking other alkylating agents such as:2
If your pet has taken chlorambucil before, but the cancer did not respond to the medication, your veterinarian will probably choose to prescribe a different chemotherapeutic agent.
Before and during your dog’s treatment, your veterinarian will order blood tests to check blood cell counts, metabolites and enzyme levels. This information is used to evaluate immune system function as well as the drug’s effect on the kidney and liver. It is important to let your veterinarian know if your pet has had a history of the following:5
Chlorambucil must be administered with extreme care, not only for your dog’s health, but for the owner’s safety. Take precautions when handling the medication:4
Although chlorambucil is well tolerated by dogs and side effects almost always disappear after treatment is complete, it is important to observe your pet for any adverse effects. Side effects from chlorambucil most often develop in the gastrointestinal tract with more serious side effects arising from bone marrow suppression. Chlorambucil may reduce blood cell production in bone marrow which reduces your pet’s capacity to fight infection and interferes with the blood clotting mechanism. If you notice any unusual bruising or bleeding, or if your pet becomes listless, shivers, and develops a fever (signs of infection), call your vet immediately.
Chlorambucil is often given in conjunction with other drugs. The most common symptoms include:3
More serious side effects include:
In case of overdose, contact your veterinarian immediately, particularly if the following symptoms occur:.5
Drug interactions may increase the risk for serious side effects or change the effectiveness of your pet’s medicine. All possible interactions cannot possibly be listed here, so be sure to keep a list of all prescription or non-prescription drugs, herbal products, and any other product that you give your pet. Share this information with your veterinarian.
Chlorambucil may react with the following drugs1
Serious interactions may occur between chlorambucil and the following drugs;6
Severe interactions can arise when combined with these drugs:6
Do not start, stop, or change the dosage of any medicines without your vet’s approval.
If your pet loses their appetite and stops eating, try the following: