(For veterinary information only)
WARNING
The size of the tablet/medication is NOT an indication of a proper dose. Never administer any drug without your veterinarian's input. Serious side effects or death can occur if you give medications to your pet without your veterinarian's advice.
It is our policy not to give dosing information over the internet.
Brand Name: Leukeran®
Available in 2 mg tablets
Background
When cancer is not localized to one area, a treatment that can reach multiple body areas, no matter how inaccessible, is needed. Surgery and radiation are therapies for localized disease and will not be helpful for more widespread tumors, but medications can travel anywhere that the body's blood vessels will take them. The use of medication to treat cancer is called chemotherapy.
For chemotherapy to be effective, the medications must destroy tumor cells and spare the normal body cells that may be adjacent. This is accomplished by using medications that affect cell activities that go on predominantly in cancer cells but not in normal cells. Most chemotherapy agents focus on the rapid cell division that characterizes the spread of cancer cells.
Chlorambucil is an alkylating agent of the nitrogen mustard group. Alkylating agents bind DNA strands so the double helix cannot “unzip” and replicate. (In other words, cell division is not possible.) Alkylating agents also bind other important biochemicals, impairing their function and even breaking DNA strands. All this DNA breakage and interference with replication make cell division particularly difficult.
There are two situations in which targeting rapidly dividing cells is necessary. As mentioned, non-localized cancer is one situation. The other is an immune-mediated disease. Immune stimulation involves rapidly dividing lymphocytes, which in turn produce antibodies and promote other immune activities. This kind of immune activity and rapid cell division are also vulnerable to drugs (like alkylating agents) that target cell division.
Alkylating agents as a group have had problems with side effects. Because chlorambucil is relatively slow-acting, fewer side effects have been an issue with this medication, especially in feline use. Chlorambucil has made the treatment of numerous cancers and immune-mediated diseases more successful, especially in cats.
Some General Information
How long it takes for medications to be cleared from the body has not been established for most drugs in veterinary medicine. Studies show detectable concentrations of drugs found in urine for days to weeks after administration, although concentrations are markedly decreased within the first three days. Many drugs are eliminated in the feces and may result in drug excretion for five to seven days after administration.
General recommendations are to handle urine and feces from patients receiving intravenous chemotherapy as contaminated for 48-72 hours after administration and for as long as seven days after oral medications.
How this Medication is Used
Chemotherapy protocols for the following cancers have included chlorambucil:
Immune-mediated conditions where chlorambucil may be especially helpful include:
Chlorambucil is typically given daily, every other day, or every third day. Pulsed dosing protocols with a higher dose every few weeks are also used in some situations. Therapeutic effects may not be seen until after two to four weeks of use, so the effectiveness of treatment should not be judged before that time.
If a dose is accidentally skipped, give the medication when it is remembered or pick it up with the next dose, allowing at least the proper interval between doses according to the label instructions.
Side Effects
The main side effect of concern with chlorambucil is bone marrow suppression. The bone marrow is the body’s source of all blood cells, both white cells and red cells. Since the precursors of these cells are rapidly dividing, they are targeted by chlorambucil. When the bone marrow is suppressed, one can develop anemia (inadequate red blood cells), a drop in white cells (which constitute the bulk of the immune system), or both. This side effect is generally evident at some point during the second week of therapy, and blood testing at this time is definitely necessary to determine if this side effect is occurring. Once the medication is discontinued, the marrow should recover in another one to two weeks, though more severe and long-lasting suppression has rarely occurred.
Poodles and Kerry blue terriers may have hair loss problems on chlorambucil, but the hair loss humans experience with chemotherapy generally does not occur with dogs and cats.
An overdose of chlorambucil results in bone marrow suppression in all cell lines, and seizures and twitching have been reported. If a pet shows neurologic signs such as these on regular dosing, chlorambucil should be discontinued.
Interactions with Other Drugs
Chlorambucil’s bone marrow suppression side effect may be compounded if chlorambucil is used with other medications that also share possible bone marrow suppression as a side effect. Such medications include:
The use of chlorambucil may lead to the need to increase the dose of allopurinol for patients who take it (such as uric acid bladder stone-forming Dalmatians).
Concerns and Cautions
How long chlorambucil will stay in your pet’s body is unknown. Because it leaves the body either in urine or feces, the amount of the drug will be at its highest level in urine or feces for the first two to three days after dosing. Because of this, during this time, your pet should not be allowed to urinate or defecate in community areas, or areas where children may be exposed, or areas that cannot be easily cleaned.
- Because sunlight can destroy drugs in the ground, the best place for your pet to urinate or defecate is in an open, sunlit area.
- Gloves should be worn whenever body fluids are cleaned up.
- For cats, litter boxes should be cleaned daily, and litter should be double-bagged in plastic bags and thrown out with the regular trash.
- If feces, urine, or vomit from your pet are found in the house, the area should be cleaned and hands should be washed immediately afterwards.
- Dilute bleach should be used to clean surfaces. Feces or materials contaminated with urine should be double-bagged in a plastic bag and disposed of in the regular trash.
- Soiled linens should be washed separately.
- Pregnant women should avoid cleaning up the body fluids.
- The DNA poisoning effects of this medication prevent its use in pregnant patients.
- Chlorambucil should not be used in patients with pre-existing bone marrow suppression.
- Chlorambucil suppresses the immune system and should be used with caution in patients already immunosuppressed (such as FIV+ cats) or with chronic infections.
- Chlorambucil may cause permanent infertility when given to patients before puberty.
Chlorambucil is best given without food, on an empty stomach. However, if your pet appears to have an upset stomach after dosing, discuss with your veterinarian if you can give it with food.
Chlorambucil should be protected from light and refrigerated. The pill should not be split or crushed.