Chemotherapy Options in Veterinary Medicine
The following article does a great job of detailing the use of chemotherapy. It is followed by a listing of chemotherapy and complementary drugs.

Chemotherapy in Veterinary Medicine
Veterinary Hospital of the University of Pennsylvania

The diagnosis of cancer is stressful for pet owners, and the prospect of chemotherapy treatments can be equally difficult. However, the fear that animals will spend most of their last days sick from chemotherapy treatments is unwarranted. Knowing how anti-cancer chemotherapy drugs work and what to expect from the treatments can help pet owners decide on whether such therapy is appropriate for their pets.

When do we use chemotherapy to treat animals with cancer?
Chemotherapy may be used as the sole treatment for certain cancers or may be used in combination with other treatment modalities, such as surgery and radiation therapy. Chemotherapy is likely to be recommended for cancer that has already spread to other areas of the body (metastatic disease), for tumors that occur at more than one site (multicentric disease), or for tumors that cannot be removed surgically (nonresectable disease). In some cases, chemotherapy can be used to try to shrink large tumors prior to surgery or to help eradicate certain types of microscopic cancer cells that cannot or have not been completely removed surgically. For cancers that are at high-risk for metastasis early in the course of disease, chemotherapy can be used after surgery or radiation therapy to help slow down the growth of cancer cells in other parts of the body.

How does chemotherapy work?
Chemotherapy drugs attack cells in the process of growth and division. Individual drugs may work through many different mechanisms, such as damaging a cell's genetic material (DNA) or preventing the cell from dividing. However, chemotherapeutic drugs cannot distinguish between malignant cancer cells and normal cells. All rapidly dividing cells are potentially sensitive to chemotherapy. Toxicity to normal, rapidly growing or self-renewing tissues in the body is the reason for most of the side effects seen with chemotherapy. Fortunately, these normal tissues continue to grow and repair themselves, so the injury caused by chemotherapy is rarely permanent.

What are the typical side effects of chemotherapy?
Compared to people who receive chemotherapy, pet animals experience fewer and less severe side effects because we use lower doses of drugs and do not combine as many drugs as in human medicine. The normal tissues that typically are most sensitive to chemotherapy are the intestinal lining, the bone marrow (which makes red and white blood cells), and hair follicles.

Toxic effects to the gastrointestinal tract are responsible for decreased appetite, vomiting, and diarrhea. These effects may be mild, moderate, or severe. In most cases, these signs are mild and usually resolve on their own or with oral medication given at home. Although infrequent, some dogs (and cats) may develop severe diarrhea requiring hospitalization and fluid therapy. In many cases, the gastrointestinal side effects from chemotherapy are not seen on the day of treatment. They often occur 3 to 5 days later.

Suppression of the bone marrow by chemotherapeutic drugs may cause a drop in the white blood cell count, leading to increased susceptibility to infection. The infection usually comes from the animal's own body (such as bacteria normally found in the intestines, mouth, skin, etc.). Severe infections may require hospitalization for intensive supportive care, including intravenous fluid and antibiotics. When a chemotherapeutic drug is used that is known to have a high potential for bone marrow suppression, a complete blood count (CBC) is checked several days after the treatment. If the white blood cell count is low but your pet is feeling well, antibiotics are prescribed as a preventative measure. Subsequent doses of chemotherapy are adjusted based on the results of the CBC. Anemia (low red blood cell count) is often a complication of cancer but is rarely caused by the chemotherapy drugs used in veterinary medicine.

Hair follicle cell in dogs (and cats) that are wire-haired or non-shedding may be particularly susceptible to chemotherapy. Certain breeds of dogs, such as terriers and poodles, will experience variable amounts of hair loss. Hair loss often is most evident on the face and tail. Whiskers and the long hairs over the eyes often fall out in cats. The hair will regrow once chemotherapy is stopped, but may initially have a modest change in color or texture.

There are many different types of chemotherapy agents and each has a different likelihood of causing side effects. If your pet is treated with drugs known to cause certain side effects, we will prescribe medications to help prevent these complications, such as antiemetics (anti-nausea and vomiting medication). In addition, we will give you instructions on what to do if and when a problem arises. We seldom see severe side effects as described above; it is estimated to be less than 5% of all pets receiving chemotherapy. With proper management, most animals recover uneventfully within a few days.

Please keep in mind that any animal can have an unexpected reaction to any medication.

How is chemotherapy given?
How a chemotherapeutic drug is administered, how often it is given and how many treatments are given varies from case to case. The type of cancer, the extent of disease, and general health of the animal help the oncologists to formulate a treatment protocol (type of drugs, dose, and schedule used) appropriate for your pet.

Some drugs are oral medications (pills) that you give at home. Others are brief injections that require an outpatient appointment. In some instances, slow infusions or repeated treatments throughout the day may require an animal to spend the day in the hospital. The treatments are typically repeated from weekly to every third week. Blood tests may be needed to monitor the effects of chemotherapy during the weeks between drug treatments.

The duration of chemotherapy depends on the type of cancer and the extent of disease. Some animals need to receive chemotherapy for the rest of their lives. In others, treatments may be spread out or discontinued after a period of weeks to months provided that the cancer is in remission, i.e., there is no detectable evidence of cancer in the body. Chemotherapy can be resumed when the cancer relapses.

We usually recommend that every patient receive at least 2 cycles of chemotherapy and then be evaluated for response before we decide to continue the treatment, change drugs or discontinue chemotherapy.

It is imperative that you, as a pet owner, are committed to treatment and that you bring your pet to the veterinary hospital when scheduled for therapy.

What can be expected from chemotherapy?
In many cases, we are unable to cure our veterinary cancer patients. Our goal is therefore to improve a pet's quality of life. To this end, chemotherapy can be used to minimize the discomfort caused by a tumor or to slow down the progression of the disease. For most (but not all) types of tumors, the oncologist will provide information on average life expectancy with and without treatments.

The decision of whether to pursue chemotherapy treatments can be complex. Medical information, practical concerns (such as need for repeated visits, your pet's temperament, etc.), and financial responsibility all play a part in this decision. We encourage you to discuss your concerns with the oncologist and/or our social worker when making this decision.

Chemotherapy Drugs
Azathioprine (Imuran) — Immune mediated diseases are conditions where the immune system becomes inappropriately active and damages the body. Azathioprine is a common medication used in the treatment of immune mediated disease. It is a drug to respect and use wisely. 

Carboplatin (Paraplatin) — Carboplatin is a platinum-containing drug used to treat malignant cancer. The drug affects the DNA of rapidly dividing cells but the exact mechanism of action is not clearly understood.

Chlorambucil (Leukeran) — A drug used most commonly for chemotherapy to treat cancer, chlorambucil is also used to treat some immune mediated diseases such as pemphigus, feline infectious peritonitous, or inflammatory bowel disease. 

Cisplatin — The treatment of cancer is scary and the word chemotherapy conjures up unpleasant images. But what are the facts of these powerful medications? Cisplatinum is an important weapon against cancer. 

Cyclophosphamide (Cytoxan) — Because of its ability to kill rapidly dividing, cyclophosphamide has been used most successfully in treating cancer and immune mediated disease. 

Cytarabine — This drug is used to treat certain cancers, most notably leukemia.

Dexamethasone (Azium, Voren) Dexamethasone is a member of the glucocorticoid class of hormones. It is utilized in the treatment of lymphoma.

Doxorubicin (Adriamycin, Rubex) — Doxorubicin is a type of anti-cancer drug called an anthracycline glycoside. It works by impairing DNA synthesis, a crucial feature of cell division, and thus is able to target rapidly dividing cells. Doxorubicin is a very serious anti-cancer medication with definite potential to do great harm as well as great good. 

Fluorouracil (5-fluorouracil, Adrucil, 5-FU) — 5-FU is an antineoplasti or cytotoxic chemotherapy drug. This medication is classified as an antimetabolite.

L-Asparaginase (Elspar) — The battle against cancer must exploit biological differences between cancer cells and normal cells. Asparagine is an especially important amino acid for lymphatic cancer cells and asparaginase is able to destroy it in a way that hurts cancer cells only. L-Asparaginase is a helpful chemotherapy agent, especially in the treatment of lymphatic cancers. 

Lomustine — Lomustine is a member of the nitrosourea class of chemotherapy agents that act by binding DNA to other DNA strands or to protein in such a way that the DNA double helix strand cannot replicate. In addition to essentially tying DNA up, lomustine generates a by-product that prevents normal DNA function. 

Piroxicam — The most common target of this medication is transitional cell carcinoma of the urinary bladder, although it is also used against mammary adenocarcinoma, squamous cell carcinoma, and transmissible venereal tumors.

Vincristine (Oncovin, Vincasar) — Vincristine is chiefly used as one drug in multi-drug combination protocols against lymphoid and round cell tumors.

Complementary Drugs

Deracoxib (Deramaxx) — Deracoxib is a member of the class of drugs known as NSAIDs, the same class as such over-the-counter remedies as Advil (ibuprofen), Orudis (ketoprofen), and aspirin. The chief use for such drugs in the dog has been pain relief, usually joint pain or post-surgical pain relief.

Diphenhydramine (Benadryl) — Diphenhydramine has several important effects and thus several uses. Most obviously, diphenhydramine is an antihistamine and it's used for acute inflammatory and allergic conditions. Mast cell tumors are tumors involving cells that contain granules of histamine. Patients with mast cell tumors experience chronic inflammatory symptoms due to circulating histamine. Antihistamines such as diphenhydramine may be helpful given long term. It also has a strong anti-nausea side effect and causes drowsiness in animals just as it does in people and can be used as a mild tranquilizer.

Fentanyl (Duragesic Patch) — The primary use of the fentanyl patch is to provide a continuous delivery of pain reliever to a patient with on-going pain. These patches are especially useful after a surgical procedure but are also helpful in the management of cancer pain, or after injury.

Metoclopramide (Reglan) — Motility disorders are common and may be chronic or of sudden onset. When motility is reduced in the stomach, food pools there and creates a sensation of nausea and bloating. In some cases, bile refluxes from the intestine into the stomach, causing irritation and more nausea. Metoclopramide (Reglan) normalizes stomach contractions so that food and bile can pass in the correct direction.

Metronidazole (Flagyl) — Metronidazole is an antibiotic especially effective against anaerobic infections. In addition, it has anti-inflammatory properties in the large intestine and is an effective anti-diarrhea medication. It's also an effective antibiotic against certain protozoal infections, especially Giardia.

Ondansetron (Zofran) — Ondansetron is used as an anti-emetic, particularly to prevent severe vomiting associated with cancer chemotherapy or radiotherapy.

Phenobarbital — Phenobarbital is probably the first choice for seizure suppression. Most often phenobarbital is used to suppress epileptic seizures (i.e., seizures for which a cause has not been identified), but phenobarbital can also be used against seizures due to brain tumors.

Prednisone/Prednisolone — Prednisone and prednisolone are members of the glucocorticoid class of hormones. They break down stored resources (fats, sugars and proteins) so that they may be used as fuels in times of stress. They are used in the treatment of lymphoma.

Silymarin (Milk Thistle) — Silymarin has been traditionally used in the treatment of liver disease and, while it has recently been advocated for use in pets, all scientific information available concerns human use. Silymarin may stabilize mast cells (cells containing inflammatory granules).


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