Overview of Chlorambucil for Canines and Felines

Chlorambucil, better known as Leukeran®, is a nitrogen mustard derivative that belongs to a group of chemicals known as alkylating agents. It is an antineoplastic and immunosuppressant for dogs and cats and works by causing cross-linking of DNA, resulting in altered protein production, decreased cell division, and cell death.

Chlorambucil is most commonly used to treat cancers of the blood and lymphatic system; however, it is also effective against some other tumors and immune-mediated conditions, such as pemphigus foliaceous and feline eosinophilia granuloma complex.

Chlorambucil is rapidly and completely absorbed from the GI tract, achieves peak plasma levels in an hour, and is transported highly bound to plasma protein (albumin).

Chlorambucil is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.

This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug

Brand Names and Other Names of Chlorambucil 

This drug is registered for use in humans only.

Human formulations: Leukeran® (GlaxoSmithKline)

Veterinary formulations: None

Uses of Chlorambucil for Dogs and Cats

Chlorambucil is used for the treatment of:

Lymphocytic leukemia

Lymphoma/lymphosarcoma

Multiple myeloma

Polycythemia vera

Macroglobulinemia

Ovarian adenocarcinoma

Immune-mediated conditions affecting skin, joints, or kidneys

Precautions and Side Effects

Chlorambucil should not be used in animals with known hypersensitivity to it or who have demonstrated resistance to it effects.

Chlorambucil should not be used in pregnant animals.

This drug can severely suppress bone marrow function and should not be used in patients with preexisting bone marrow depression or infection. Anemia, leucopenia, and thrombocytopenia may occur as a result of chlorambucil treatment.

Gastrointestinal side effects may occur including anorexia, vomiting and/or diarrhea.

Neurotoxic side effects of chlorambucil may include such as myoclonus, tremors, muscular twitching, agitation, and tonic-clonic seizures.

Chlorambucil may cause alopecia or delayed re-growth of shaven hair. This side effect is thought to be more common in Poodles and Kerry Blue terriers. Biochemically, hyperuricemia may occur during treatment with chlorambucil so serum uric acid should be monitored. Allopurinol or probenecid may be needed to correct this aberration.

It is also recommended to monitor the complete blood count (CBC) and liver function during therapy.

Drug Interactions

Chlorambucil may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with chlorambucil.

Chlorambucil’s use with other myelosuppresant agents will increase the degree of bone marrow suppression and increase the risk of concurrent infection.

How Chlorambucil is Supplied

Chlorambucil is is available in 2 mg – white, sugar coated tablets.

Dosing Information of Chlorambucil for Dogs and Cats

Medication should never be administered without first consulting your veterinarian.

Doses of chlorambucil vary widely depending on the reason for prescribing.

The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse.

In dogs, the usual dose is 0.1 mg per pound (0.2 mg/kg) orally for 14 days then 0.05 mg per pound (0.1 mg/kg). It may be used with tapering doses of prednisone.

In cats, the usual dose is 0.05 to 0.1 mg per pound (0.1 to 0.2 mg/kg) orally daily. Alternatively, it may be dosed at 0.125 to 0.25 mg per pound (0.25 to 0.5 mg/kg) every 48 to 72 hours.