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Chemotherapy for Dogs - Side Effects and Medications

María Besteiros
By María Besteiros, Expert veterinary assistant and canine/feline hairdresser.. February 18, 2019
Chemotherapy for Dogs - Side Effects and Medications

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Chemotherapy for dogs, as with humans, is an intensive course of canine cancer treatment. While often successful in treating certain cancers, especially if diagnosed early enough, it can also be debilitating and painful. For dogs, they are unlikely to understand why they are being made so ill, even if it is for their benefit. For guardians of dogs, this can raise certain questions over the best course of treatment in terms of quality of life. There is also the financial consideration which can make decisions even more difficult as cost of chemo drugs is not cheap.

In this AnimalWised article on chemotherapy for dogs we look at the side effects and medications involved in this type of cancer treatment. Before we discuss whether chemotherapy is even suitable for your dog, you need to know the importance of speaking to a veterinarian. We will discuss the advantages and disadvantages of its use, taking into account the characteristics of the cancer and condition of the dog.

  1. What is chemotherapy for dogs?
  2. How does chemotherapy for dogs work?
  3. Chemotherapy protocols in dogs
  4. Metronomic chemotherapy in dogs
  5. Side effects of chemotherapy for dogs
  6. Combination of drugs for chemotherapy in dogs
  7. What is a chemotherapy session like for a dog?
  8. Care during and after chemotherapy for dogs

What is chemotherapy for dogs?

When a dog is diagnosed with cancer, the first option for treatment is likely to be surgery. However, after surgical intervention, other forms of treatment may be required to avoid recurrence of the cancer or delay any possible metastases (spreading of the cancer). Chemotherapy is also sometimes used to reduce a tumor's size before surgery. Palliative chemotherapy is used not to treat the dog's cancer, but to reduce the symptoms and to try to improve the quality of life during their final days.

Chemotherapy involves using anti-cancer drugs to either attempt to cure the cancer or improve their quality of life. Unlike other types of cancer intervention, because the drugs are introduced to the bloodstream, they can affect any part of the body affected by cancer.

Palliative chemotherapy is something which many dog owners may not even be able to afford. If they can, it may be possible to prolong the life of the dog, but there are no guarantees. The cost of chemotherapy for dogs may be prohibitive, but a report from 2003 looked into the owner's assessment of their dog's quality of life during palliative chemotherapy for lymphoma[1]. It claimed that, although 52% of owners experienced complications during the dog's treatment, 92% had no regrets about initializing chemotherapy treatment.

Since the cost of chemotherapy for dogs is often so high, many guardians ask is chemotherapy for dogs worth it? If this is something you are considering, then you will have to assess your circumstances. It will rely on the individual dog and how your feelings match up to your resources.

How does chemotherapy for dogs work?

The drugs used for canine chemotherapy treatment are going to mainly act on the cells which are undergoing division. As cancer is defined by an uncontrollable cell growth, chemotherapy is designed to attack and eliminate tumor cells.

Part of the complication of chemotherapy treatment for dogs is that this attack is not selective. The drugs will act not only on the tumor cells, but also on healthy cells. This is particularly the case with cells in the intestine and the bone marrow as these are the ones which undergo most division. As we will see, it is the action of chemotherapy drugs which are responsible for any adverse reactions.

Chemotherapy for Dogs - Side Effects and Medications - How does chemotherapy for dogs work?

Chemotherapy protocols in dogs

In general, chemotherapy is prescribed at the maximum tolerated dose (MTD) and their affect will depend on the level of this dosage. Sessions are usually established on a regular basis every 1 to 3 weeks, but will depend on the speed of recovery of their tissues. Veterinarians follow standardized doses which have been well-studied in terms of tolerance levels. A recent study from 2018 evaluated the safety of carboplatin and toceranib phosphate in tumor bearing dogs[2], showing there is always development in assessment of new medications.

With the exception of certain cancer types, such as transmissible venereal tumors where a single drug type may be effective, in most cases it will take a combination of drugs. In this way, chemotherapy treatment adapts to the characteristics of the cancer and the dog in order to achieve the best results.

Metronomic chemotherapy in dogs

Veterinary oncologists have begun to use something known as metronomic chemotherapy, although it is still in its experimental stages. It aims to inhibit the formation of blood vessels that develop tumors by providing nutrients for their growth. This type of therapy usually has less expensive as the chemotherapy drugs come at a cheaper price and can be administered without the necessity of hospitalization.

In contrast to chemotherapy using the maximum tolerated dose, metronomic chemotherapy is based on a low dose course administered daily. The administration is either oral, intravenous, intracavitary or intratumoral. Currently, it also works with targeted chemotherapy capable of selecting its action on specific tissues. It thereby minimizes side effects. According to a review in 2017[3], the benefits of metronomic chemotherapy include:

  • Better tolerability and reduced need for supportive medications
  • Generally lower cost
  • Increased convenience as pets can be kept at home
  • Less stress to the animal
  • Lower probability of drug resistence
  • Potential for combination with other drugs

Side effects of chemotherapy for dogs

As we have stated, chemotherapy can affect healthy cells, especially those located in the intestine and bone marrow. Adverse effects, therefore, most often tend to be related to these parts of the body. This is why we may see gastrointestinal disorders, anorexia, vomiting or diarrhea as side effects. The chemotherapy medication also may lead to a decreased number of leukocytes which increases the likelihood of infection, decreases platelet levels and may induce fever. The coloration of their urine may vary.

Additionally, depending on the drugs used, other symptoms may present. These include cystitis, cardiac problems, dermatitis and even local necrosis if the product leaves the vein or causes allergic reactions. The appearance of these side effects is influenced by other factors such as the breed of dog (as it may hinder the metabolism of certain drugs), if it suffers from other diseases or if they are taking other medications.

The most serious side effect of chemotherapy in dogs is the decreased in leukocytes. To combat this problem and other related issues, we can use other drugs concurrently, even ones administered preventively. If the dog is losing their appetite, we can offer better quality or more appetizing food. Diarrhea will usually solve itself after treatment. Allowing them more opportunity to go outside to urinate can reduce the potentiality of cystitis. All of these adverse effects can occur, so we should be prepared to manage them.

Chemotherapy for Dogs - Side Effects and Medications - Side effects of chemotherapy for dogs

Combination of drugs for chemotherapy in dogs

We have already seen that is is common practice to combine several drugs to formulate a specific chemotherapy treatment for cancer in dogs. The veterinarian will be able to choose this combination according to various factors. This will depend on the drugs available in a specific market, the clinical picture of the dog and, importantly, which drugs have shown most efficacy against a particular type of cancer. Also, each drug has its own mechanism of action, so they need to compliment each other and not present overlapping toxicities.

What is a chemotherapy session like for a dog?

A typical chemotherapy session for dogs will take place in a veterinary clinic, but not every clinic will be suitable. This means the session may need to take place in a veterinary hospital. The first step is to do a blood test to assess the dog's general condition. Drugs should be prepared with precautions due to their toxicity, especially in avoiding inhalation or touching them accidentally.

In intravenous chemotherapy, a professional will be required to ensure the line is perfectly placed in the vein. The line will preferably be placed in the front leg to avoid adverse effects caused by coming in contact with it. The leg is usually wrapped in gauze and bandages to protect it and reduce leakage.

The administration of chemotherapy in dogs is performed carefully, but the length of administration will depend on the individual drug. This can be a single injection which takes a matter of seconds, but most will take at least a few minutes. Some may take longer, but this type of chemotherapy treatment is rare. It is most important that the administration works properly. The dog needs to be calm and may be likely sedated. The vet or similar professional should be present to control the situation at all times. At the end of the medication application, they may continue with fluid therapy to clean the site and remove traces of the drugs. After this session, the animal will usually go back home and have little adverse effects.

Chemotherapy for Dogs - Side Effects and Medications - What is a chemotherapy session like for a dog?

Care during and after chemotherapy for dogs

Before starting chemotherapy, the veterinarian may prescribe some drugs to try to avoid side effects. If the session takes place in a clinic, the professionals will take care of all of the precautions and care needs. If we are the ones who must treat the dog with oral chemotherapy at home, it is important we always use gloves. We should never break to pills and, of course, given by the vet. Pregnant women should not handle chemotherapy drugs.

After chemotherapy, we need to carefully monitor the dog's temperature. We need to do the same for any abnormal symptoms and carefully administer any prescribed drugs. Your dog should not feel any adverse effects after the initial administration, but they may start to exhibit some effects after 3 to 5 days. This effects should disappear within 24 hours and most dogs will not exhibit any symptoms.

If we need to lift or remove the dog's feces, we need to wear gloves for at least 48 hours after administration. Chemotherapy drugs are eliminated from the body in 2 to 3 days, but in minimal quantities. We need to ensure we take no risks with their basic hygiene routine and not leave feces out in public.

Chemotherapy for Dogs - Side Effects and Medications - Care during and after chemotherapy for dogs

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to Chemotherapy for Dogs - Side Effects and Medications, we recommend you visit our Other health problems category.

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Chemotherapy for Dogs - Side Effects and Medications