(for veterinary information only)

BRAND NAME: ONCOVIN, VINCASAR

AVAILABLE AS INJECTABLE

BACKGROUND

Because they are transported everywhere that the bloodstream can take them, drugs of cancer chemotherapy have the ability to reach tumors that are inaccessible to the surgeon and undetectable to the diagnostician. In order to spare the normal cells of the body, anti-cancer drugs must affect activities that cancer cells are involved in but normal cells are not. Since cancer cells divide rapidly and uncontrollably while normal cells divide more slowly and in response to controlled cellular messages, most anti-cancer drugs target cell division.

As a cell divides, microscopic protein rods, called “microtubules,”  pull the two cell halves apart. These important structural proteins must be functional or cell division cannot occur.  Vincristine is a member of the “vinca alkaloid” class of chemotherapy drugs. It is extracted from the Vinca rosea plant and is a microtubule poison.

HOW THIS MEDICATION IS USED

Vincristine is chiefly used as one drug in multi-drug combination protocols against lymphoid and round cell tumors. Lymphoma, Mast Cell Tumors, and Transmissible Venereal Tumors often include vincristine in their protocols.

Separate from its chemotherapy use, vincristine has the unexplained ability to cause a sudden release of platelets (blood clotting cells) from the bone marrow. For this reason, vincristine is commonly included in treatment of immune-mediated thrombocytopenia or ( ITP”).  There has been some controversy about whether these platelets are as functional as normal ones but current published protocols for this condition suggest vincristine should be used.

Vincristine is typically utilized as a weekly injection.

SIDE EFFECTS

Vincristine must absolutely be given intravenously. Vincristine is highly irritating to the soft tissues and if it is not given intravenously, where the bloodstream rapidly carries it away and dilutes it within the body’s blood volume, it will cause what is called a “tissue slough.” This means the soft tissues will die and fall away leaving a large sore. Unlike the tissue sloughs of Adriamycin, a vincristine slough will eventually heal but while it is present, it will require bandaging and be a source of discomfort.

Vincristine has some potential for neurologic side effects, especially in cats. A neurologically based constipation may result. Difficulty coordinating the feet may be seen. Humans report “paresthesias” which include odd sensations such as occur when one’s foot is “asleep.”

Vincristine use will increase blood uric acid levels, rarely a concern in animals.

INTERACTIONS WITH OTHER DRUGS

The neurologic toxicities noted above are more likely to occur when vincristine is used in combination with L-Asparaginase, not an uncommon combination in the treatment of lymphoma.

CONCERNS AND CAUTIONS

Vincristine is not able to pass through the blood/brain barrier and thus cannot treat tumors in the nervous system.

Vincristine is removed from the body by the liver. If poor liver function is present, a dose-adjustment may be needed or a different drug selected.

Vincristine should not be used in pregnancy and may cause sterility in males.