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The treatment of cancer with medication (as opposed to surgery or radiation) is especially helpful when the cancer in question is not localized to one body area. Using medication allows the body’s blood vessels to carry the medication to even remote or otherwise inaccessible areas. This form of treatment is called “chemotherapy.”
In order for chemotherapy to be effective, the medications must detroy tumor cells and spare the normal body cells which 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 what is called an “alkylating agent” of the “nitrogen mustard” group. Alkylating agents work by binding DNA strands so that 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 can even break DNA strands. All this DNA breakage and interference with replication makes cell division particularly difficult.
Tissues with rapidly dividing cells, such as cancer tissues, are especially vulnerable. In particular, lymphocytes, whose normal function involves rapid division, antibody production and immune activities, are also very sensitive to the effects of alklyating agents thus making the alkylating agents particularly helpful in treating non-cancerous immune-mediated diseases (i.e. disease where the immune system erroneously attacks the body). In other words, cancer is not the only illness that can be treated with chlorambucil, immune-mediated diseases are also susceptible.
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. The use of chlorambucil has made the treatment of numerous cancers and immune-mediated diseases more successful especially in cats.
Chemotherapy protocols for the following cancers have included chlorambucil:
Immune Mediated conditions where chlorambucil may be especially helpful include:
Chlorambucil is typically given daily or every other day or every third day.
The main side effect of concern with chlorambucil is bone marrow suppression. The bone marrow is one’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 an anemia (inadequate amount of 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 in order to determine if this side effect is occuring. Once the medication is discontinued, the marrow should recover in another 1-2 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.
Overdose of chlorambucil results in bone marrow suppression in all cell lines as well as seizuring.
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).
The DNA poisoning effects of this medication precludes its use in pregnant patients; further, pregnant women should not handle this medication, nor the urine/feces of animals taking chlorambucil.
Chlorambucil should not be used in patients with pre-existing bone marrow suppression.
Chlorambucil is suppressive to the immune system and should be used with caution in patients already immune suppressed (such as FIV+ cats) or with chronic infections.
Chlorambucil may cause permanent infertility when given to patients prior to puberty.
Page last updated: 2/20/2012