Chemotherapy Injections vs. Oral Medications: Which Is Right for Your Dog?

Thankfully, chemotherapy treatments that are designed for dogs are planned around keeping them as comfortable as possible. Most dogs tolerate chemotherapy very well and we are able to provide more good days. Especially because dogs are not able to communicate if they are feeling uncomfortable or ill—nor do they understand why they are getting treatment—the way that human chemotherapy patients can. Though the goal is to mitigate as many of the side effects of treatment as possible, some dogs do still experience side effects. That said, the method of delivering chemotherapy treatment can make a difference in what side effects are experienced and to what degree. 

There are two common delivery methods of chemotherapy treatment for canine cancer patients: cytotoxic injections and oral medications. 

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What are Cytotoxic Chemotherapy Injections? 

Cytotoxic means that a substance is toxic to living cells, and because cancer cells are living cells, that means that chemotherapy falls into the cytotoxic category. Specifically, all chemotherapy drugs are designed to target rapidly dividing cells in the body, and while most of these cells are cancerous, there admittedly will be some healthy cells that are affected by the medication.  

Injectable chemotherapy is administered by a veterinarian; most often it is delivered via catheter into a vein, however some cancer and drug combinations are more effective if delivered subcutaneously (under the skin) or intramuscular (into a muscle), and in highly specific cases there are some treatments that require the medication to be administered directly into the tumor. 

Cancers that are generally treated with chemotherapy injections include: Lymphoma, Osteosarcoma, Hemangiosarcoma, and high grade Mast Cell Tumors. In some cases also: Soft tissue Sarcoma, Transitional cell carcinomas, high grade Mammary Carcinomas, and other metastatic cancers.

Some examples of chemotherapy drugs in this category include: Doxorubicin, Vincristine, Mitoxantrone, Tanovea, Mechlorethamine, and Vinblastine. 

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What Makes Oral Chemotherapy Medications Different

One of the major differences with oral chemotherapy medications is that pet parents are able to administer these at home, putting them in charge of the dosing schedules and adding some additional safety precautions to the pet parent’s routine. 

Oral chemotherapy can be the primary method of treatment or given in combination with other injectable drugs to create a protocol for the individual patient. For some patients, their treatment can exclusively include oral chemotherapy, for financial, temperamental, and/or medical reasons—all of which are equally viable considerations to how a chemotherapy treatment is designed. 

Some examples of chemotherapy drugs in this category include: Chlorambucil, Cyclophosphamide, Lomustine, and Melphalan. 

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Pros and Cons of Oral Chemo vs. Injections 

It’s important to take all aspects of your pet’s needs and situation into consideration when it comes to choosing their treatment. Depending on what kind of cancer they have, there is a chance that your vet will recommend a specific chemotherapy drug for its unique purpose in helping your dog through their cancer journey. However, there are some medications that can be used in tandem, or to replace another for many reasons: including owner’s preference, patient’s temperament, and cost efficiency.  While it is always helpful to learn as much as you can to support your pet, it’s also important to trust that your vet has their best interest in mind as well, and the expertise to back it up. 

Pros and Cons of Oral Chemotherapy Medications

PROS

• Convenient at-home administration: No need for frequent vet visits, which is ideal for dogs with anxiety and/or mobility issues.
• Less stress on your dog: Many pets tolerate pills or capsules better than repeated trips to the vet, along with IV drug administration. 
• Flexible dosing: Some chemotherapy protocols can be paused or adjusted to manage side effects.
• Good option for long-term, low-dose maintenance therapy: for cancers that are less aggressive or slow growing, some dogs may benefit from a lower intensity treatment. Examples would be small-cell lymphoma 

CONS

• Strict handling precautions for household: It’s important to remember chemotherapy drugs are cytotoxic—which can and will affect cells other than the patients if encountered improperly. Caregivers must wear gloves and wash hands thoroughly after administering, and additional care may be required by the rest of the household.
• Missed doses can reduce effectiveness: Owners must be consistent and follow dosing instructions carefully.
• Cyclophosphamide specifically, can cause bladder irritation leading to additional observation: some drugs require additional meds or “bladder flushing walks” to support your dog’s comfort and keep your home clean.
• Risk of accidental ingestion: Other pets or children in the home may be at risk if pills are dropped or improperly stored which requires additional diligence in households with other animals and young children. 

Pros and Cons of Cytotoxic Chemotherapy Injections 

PROS

• Veterinarian-controlled administration: reduces risk of missed or improperly handled doses
• Higher drug precision and absorption: Injections can provide stronger and faster delivery into the bloodstream 
• Less day-to-day responsibility for owners: you don’t need to worry about managing pill schedules or handling medications at home 
• Ideal for aggressive or fast growing cancers:  Many are added to combination protocols (Such as CHOP protocol for canine lymphoma)
• Flexible dosing is also available to help manage symptoms 

CONS

• More frequent vet visits: Depending on the drug, your dog may need to visit the clinic weekly or biweekly. 
• Higher stress for anxious pets: the process of travel, restraint,and injection may be uncomfortable for some dogs
• Greater risk of acute side effects: injections like Doxorubicin may cause nausea, diarrhea, or immune suppression within days. 
• More expensive in some cases: Costs may be higher due to clinic time, monitoring, and drug administration fees. 

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Comparing Side Effects 

There is a lot of overlap in the side effects any dog may experience undergoing chemotherapy from either form of treatment. It’s a common belief that oral chemotherapy will have less acute side effects than a comparable treatment given through injections. While it’s easy to make the logical leap that the higher absorption rate provided by injections would lead to a higher likelihood of side effects, often it depends on the individual patient’s reaction more than the drug itself. The “dose makes the poison” so the amount of drug in the body also affects the rate of side effects and toxicity.

The most common side effects that dogs experience from chemotherapy treatment—and it’s important to note: not all dogs experience all of these side effects, some may not experience any—include stomach upset, lethargy or fatigue, and a lowered immune system. Many of these side effects come from the specific combination of chemotherapy drugs used in your dog’s treatment; the drugs are affecting the cancerous cells in the body but will also have an impact on some healthy cells as well, which is what leads to these side effects. 

Some side effects that are specific for each form of treatment involve smaller scale issues like a dog having sensitivity around their injection site, or slightly more stomach irritation from a specific oral medication. 

You can learn more about chemotherapy side effects and how to manage them in our post here. 

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Caring for a Dog in Chemotherapy Treatment 

In general, when you have a pet undergoing chemotherapy of any delivery method it’s important to keep track of their needs and any changes they go through. It’s crucial to keep your pet’s well-being in mind and communicate with your vet when you have concerns or questions so that you’re supporting the work the vet is doing while your pet is at home with you. 

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Finding The Best Possible Chemotherapy Treatment For Your Pooch

There are a lot of factors that go into developing a chemotherapy treatment plan for a patient. Some veterinarians will base their plans on peer reviewed studies, others may do a little bit more personalizing for the individual patient. There are many cancers that will respond well to treatment being given based on what the veterinary oncologist knows has worked in the past, but there are others, like canine lymphoma, that benefit from an individual approach. 

ImpriMed is here to help you get the best treatment for your dog when they’re diagnosed with canine lymphoma by putting the best possible drug combinations into your vet’s hands. By using advanced technology, a database of past canine lymphoma patients and treatment plans, and your pet’s living cancer cells, ImpriMed uses an AI algorithm to create a Personalized Prediction Profile. This Profile outlines the drug or combination of drugs that will be the most efficient for treating your pet as well as outlining a timeline to remission. Finding the scientifically-chosen, best treatment for your pet’s needs helps to mitigate the stress of making the right decision for their treatment. 

Learn about how you can get your vet involved with ImpriMed here.

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