What Medications Are Commonly Prescribed for Dogs With Cancer?

Dogs with cancer are usually prescribed medications from three distinct groups, and it helps to know which is which.

Drugs that treat the cancer itself — conventional chemotherapy agents such as doxorubicin, vincristine, cyclophosphamide, carboplatin, and lomustine; targeted therapies such as toceranib (Palladia); newer approved options including rabacfosadine, verdinexor, and tigilanol tiglate; immunotherapies such as gilvetmab and the Oncept melanoma vaccine; and prednisone, which acts against several cancer types directly.

Drugs that prevent or manage side effects — anti-nausea medications such as maropitant and ondansetron, appetite stimulants such as capromorelin and mirtazapine, anti-diarrheals, and sometimes antibiotics.

Drugs that keep a dog comfortable — pain medications, anti-inflammatories, stomach protectants, and antihistamines.

Two things surprise most owners. First, most of these are human drugs used off-label in dogs, which is entirely normal in veterinary oncology and not improvised. Second, veterinary chemotherapy is deliberately dosed lower than human chemotherapy, because the goal is quality of life rather than maximum tumor kill. Roughly 15–30% of dogs experience any side effects, and most are mild; severe effects requiring hospitalization occur in around 5–7% of cases.

This article describes what these medications do in general terms. It does not give doses, and no medication here should be given without your veterinarian's direction.

Key points

• Chemotherapy in dogs is not chemotherapy in people. Doses are chosen to preserve wellbeing, and most dogs continue normal life during treatment.
• Only one oral targeted drug, toceranib, is FDA approved for canine cancer in the US — most other chemotherapy agents are human drugs used off-label, which is standard practice.
• Prednisone and NSAIDs must not be given together. This combination causes gastrointestinal ulceration, and a washout period may be needed when switching.
• Some breeds carry the MDR1 gene variant, which changes how certain chemotherapy drugs are handled. Herding breeds are most affected, and testing is available.
• Preventing side effects works better than treating them. Anti-nausea drugs given proactively after chemotherapy reduce nausea and protect appetite.
• Ask for "just in case" medications to keep at home, so you can act if problems start after hours.
• Handle your dog's waste with gloves for 72 hours after chemotherapy, and wear gloves when giving oral chemotherapy tablets.
• Never split or crush oral chemotherapy tablets, and never let a pregnant, breastfeeding, or immunocompromised person handle them.

Detailed explanation

Drugs that treat the cancer

Conventional chemotherapy works by damaging rapidly dividing cells. Because some healthy cells also divide quickly — bone marrow, the gut lining, hair follicles — these are the tissues where side effects appear. Treatments are spaced to let those normal cells recover.

The agents most commonly used in dogs:

• Doxorubicin — lymphoma, osteosarcoma, hemangiosarcoma, various carcinomas and sarcomas. Given intravenously. It carries a lifetime cumulative limit because of potential heart effects, so your oncologist tracks total dose received.
• Vincristine — lymphoma, mast cell tumors, transmissible venereal tumor, leukemia. Less suppressive of bone marrow than related drugs.
• Cyclophosphamide — lymphoma, carcinomas, sarcomas. Oral or intravenous. Can irritate the bladder lining, which is why extra water access and frequent walks for a few days after treatment are recommended.
• Carboplatin — osteosarcoma, melanoma, carcinomas. Its effect on white cell counts comes later than most drugs, typically around 10 to 14 days.
• Lomustine (CCNU) — lymphoma, mast cell tumors, brain tumors, histiocytic sarcoma. Given as a capsule at home. Requires liver monitoring.
• L-asparaginase — lymphoma and leukemia. Barely affects the bone marrow at all, but can cause allergic reactions.
• Vinblastine, chlorambucil, mitoxantrone — used for specific tumor types, with chlorambucil often chosen for slow-moving disease such as chronic lymphocytic leukemia.

Several of these are given in combination. CHOP — the standard lymphoma protocol — combines cyclophosphamide, doxorubicin, vincristine, and prednisone over several months.

Newer approved options have expanded what is available:

• Rabacfosadine — FDA approved for canine lymphoma, given intravenously. Not used in West Highland white terriers.
• Verdinexor — conditionally FDA approved for canine lymphoma, given orally with food.
• Tigilanol tiglate — FDA approved for certain non-metastatic mast cell tumors of the skin, injected directly into the tumor. It works by causing the tumor to break down, so a wound forms at the site and is expected rather than a complication. It must be given alongside other medications to control the effects of mast cell degranulation.

Targeted therapy works differently, blocking specific signalling pathways rather than attacking dividing cells broadly.

Toceranib (Palladia) is the only oral targeted drug FDA approved for canine cancer in the United States, licensed for recurrent grade 2 and 3 mast cell tumors. It is also used off-label for a range of other cancers including anal sac carcinoma, thyroid carcinoma, and heart-base tumors. It is given at home, and requires monitoring of bloodwork, weight, blood pressure, and urine protein. Diarrhea and appetite loss are its most common side effects.

Immunotherapy enlists the dog's own immune system.

• Gilvetmab is an antibody that blocks a mechanism tumors use to hide from immune cells, conditionally licensed for canine mast cell tumors and melanoma. It is currently available only through oncologists.
• The Oncept canine melanoma vaccine is USDA licensed for malignant melanoma and works best once local disease has been controlled. It requires a special injection device and is only available from a specialist.

Metronomic chemotherapy deserves separate mention because it looks different from what owners expect. Rather than periodic high doses, it involves a low dose of an oral chemotherapy drug — usually cyclophosphamide — given daily or every other day at home, generally alongside an NSAID. The aim is to stabilize disease by interfering with the tumor's blood supply rather than to shrink it. Side effects are usually mild, costs are lower, and it is often considered when conventional protocols are declined or have stopped working.

Prednisone and prednisolone blur the categories. These steroids act directly against lymphoma, mast cell tumors, myeloma, and chronic lymphocytic leukemia. They are also used for entirely different reasons — reducing swelling around brain tumors, managing high blood calcium, and supporting appetite and comfort.

They reliably cause increased thirst, urination, and appetite, along with panting and, over time, muscle loss. These are expected effects rather than warning signs. The critical rule is that prednisone must not be combined with NSAIDs — the two together significantly raise the risk of gastrointestinal ulceration, and a washout period is often needed when switching between them.

Drugs that prevent and manage side effects

This group matters more than owners often expect, because one of the most common reasons families stop cancer treatment early is that their dog is not eating — a problem that is usually manageable.

Anti-nausea medications:

• Maropitant — the mainstay. Often given by injection before treatment for higher-risk drugs, and orally for four to five days afterward to prevent delayed nausea.
• Ondansetron — used for nausea occurring soon after treatment.
• Metoclopramide — another option, sometimes used alongside the others.

Nausea in dogs frequently occurs without vomiting, and the classic sign is a dog that approaches its food, sniffs, and turns away.

Appetite stimulants:

• Capromorelin — an oral solution that mimics the body's own hunger signal.
• Mirtazapine — an older medication with appetite-stimulating effects.

Both may be used alongside anti-nausea medication. Current guidance is clear that if nausea may be driving the appetite loss, the nausea should be treated first.

For diarrhea: dietary changes and probiotics, crofelemer, and in some cases specific antibiotics. Notably, current guidelines have moved away from routinely reaching for antibiotics for post-chemotherapy diarrhea, partly to avoid disrupting gut bacteria.

Antibiotics are used when white cell counts drop low enough to risk infection. Trimethoprim sulfamethoxazole and amoxicillin-clavulanic acid are common choices. Some oncologists prescribe them preventively around the expected low point after highly suppressive drugs, though this practice is debated.

Stomach protectants — omeprazole, famotidine, sucralfate — are used when ulceration is a risk, particularly with mast cell tumors, where antihistamines such as diphenhydramine are also commonly prescribed to counter the histamine those tumors release.

Drugs for comfort

Pain control is treated as central rather than optional, and a multimodal approach — combining several medications with different mechanisms — is standard.

• NSAIDs such as carprofen, meloxicam, and piroxicam. Piroxicam has a particular role in urothelial (bladder) carcinoma, where it has anti-cancer activity of its own. Remember the rule about not combining these with steroids.
• Gabapentin or pregabalin, with mixed evidence but a reasonable role as an add-on.
• Opioids including buprenorphine and stronger agents for more severe pain.
• Bedinvetmab, a monoclonal antibody given by injection for chronic pain in dogs.
• Bisphosphonates, given intravenously, which reduce bone pain and are used for cancers involving bone.

Where pain is driven by the tumor itself and cannot be controlled by medication, palliative-intent radiation is often the most durable option — evidence from human and animal studies suggests 70–90% of patients with cancer-related pain get significant relief.

Why the doses are lower than in human medicine

This is worth stating plainly, because owners often decline chemotherapy based on what they have seen in people.

Veterinary chemotherapy protocols are designed around maintaining quality of life, not around achieving cure at any cost. Roughly 15–30% of dogs experience any side effects, most of them mild and short-lived — vomiting, diarrhea, or a few flat days. Severe effects requiring hospitalization occur in around 5–7% of cases, and most dogs complete their protocol without dose changes.

Hair loss is uncommon in dogs, since most breeds do not have continuously growing coats. Breeds that do — poodles, some terriers — may thin, and whiskers may be lost, with regrowth after treatment sometimes in a different texture or colour.

The MDR1 gene

Some dogs carry a variant of the MDR1 gene that changes how their bodies handle certain drugs, including several chemotherapy agents. Herding breeds are most commonly affected — Collies, Australian Shepherds, Shetland Sheepdogs, Border Collies, and related breeds, including mixes.

Testing is available and inexpensive. If your dog is a herding breed or mix and chemotherapy is being considered, it is worth asking about.

Handling these medications safely at home

Chemotherapy drugs are classed as hazardous, and exposure risk does not stop at the clinic door. Current guidelines give specific advice for owners:

• Avoid contact with your dog's urine and feces for 72 hours after chemotherapy. If cleanup is unavoidable, wear gloves and a mask.
• Wear gloves when handling oral chemotherapy tablets, and do not handle them in kitchens or food preparation areas.
• Never split or crush these tablets. Compounded liquid versions exist but are not recommended because of exposure risk.
• Anyone pregnant, trying to conceive, breastfeeding, or immunocompromised should not handle these drugs or the waste of a treated dog.

Ask your practice for written instructions specific to the drugs your dog is on. If cleanup happens in the garden or a shared space, ask how to manage that too.

Practical things worth asking for

"Just in case" medications. Guidelines specifically recommend sending chemotherapy patients home with medications for side effects, so that problems arising after hours can be treated promptly rather than becoming emergency visits. If you have not been offered these, ask.

A written medication schedule. Dogs on treatment can be taking six or more medications on different schedules. A printed chart reduces errors considerably.

Clear thresholds. For each drug, ask what should prompt you to stop giving it and call. For toceranib, for example, specific thresholds exist — more than two episodes of vomiting or diarrhea in 24 hours, appetite loss, or fresh blood in the stool for more than two days.

A single list to carry. Emergency clinics and other practices need to know everything your dog is taking, particularly before prescribing anti-inflammatories.

When to contact a veterinarian

Seek emergency care immediately if your dog:

• Has a fever, particularly within about two weeks of chemotherapy — febrile neutropenia is an oncologic emergency requiring hospitalization
• Is vomiting blood, or passing black tarry stool
• Cannot keep water down
• Is collapsed, very weak, or has pale gums
• Has swelling, redness, or blistering at the site where an intravenous drug was given
• Has a severe allergic reaction — facial swelling, hives, difficulty breathing

Contact your veterinarian within a day if your dog:

• Has vomited more than twice in 24 hours, or has persistent diarrhea
• Has stopped eating, or is eating noticeably less
• Is unusually flat or tired, especially in the week after treatment
• Is straining to urinate or has blood in the urine — possible bladder irritation from cyclophosphamide
• Has fresh blood in the stool while on toceranib
• Has developed a new lump, swelling, or skin change
• Seems unwell in a way you cannot explain

Contact your veterinary team before:

• Giving any new medication, including anything over the counter
• Accepting a prescription from another practice, especially an anti-inflammatory
• Starting any supplement — some interact with chemotherapy drugs
• Stopping any medication yourself, particularly steroids, which should not be stopped abruptly

Questions to ask your veterinarian

• What is each of these medications for, and which are treating the cancer versus managing side effects?
• Which are hazardous drugs, and what precautions do I need at home?
• Can you write out a schedule showing what to give when?
• What side effects should I expect from each, and when are they most likely?
• What should make me stop a medication and call you?
• Can I have "just in case" medications for nausea, appetite, and diarrhea?
• Are any of these drugs unsafe to combine, and is there anything I should never give?
• Should my dog be tested for the MDR1 gene variant?
• Is my dog on both an NSAID and a steroid — and if a change is needed, how do we manage the switch?
• What monitoring tests are needed, and how often?
• If cost is a constraint, which medications matter most?

Sources

Christensen, J., Johnson, K., Ettinger, S., Garrett, L., Gordon, I., Ireifej, S., Love, A., & Wisecup, M. (2026). AAHA oncology guidelines for dogs and cats. Journal of the American Animal Hospital Association, 62(1), 1–37. https://doi.org/10.5326/JAAHA-MS-7549

American Animal Hospital Association. (2026). 2026 AAHA oncology guidelines for dogs and cats: Therapeutic modalities — chemotherapy. https://www.aaha.org/resources/2026-aaha-oncology-guidelines-for-dogs-and-cats/section-5-therapeutic-interventions/therapeutic-modalities-chemotherapy/

American Animal Hospital Association. (2026). 2026 AAHA oncology guidelines for dogs and cats: Section 7. Supportive and symptomatic care. https://www.aaha.org/resources/2026-aaha-oncology-guidelines-for-dogs-and-cats/section-7-supportive-and-symptomatic-care/

American Animal Hospital Association. (2022). 2022 AAFP/AAHA antimicrobial stewardship guidelines. https://www.aaha.org/resources/2022-aafpaaha-antimicrobial-stewardship-guidelines/

Chavalle, T., Chamel, G., Denoeux, P., et al. (2022). Are severe adverse events commonly observed in dogs during cancer chemotherapy? A retrospective study on 155 dogs. Veterinary and Comparative Oncology, 20(2), 393–403.

Elmslie, R. E., Glawe, P., & Dow, S. W. (2008). Metronomic therapy with cyclophosphamide and piroxicam effectively delays tumor recurrence in dogs with incompletely resected soft tissue sarcomas. Journal of Veterinary Internal Medicine, 22(6), 1373–1379.

Fournier, Q., Serra, J. C., Handel, I., et al. (2018). Impact of pretreatment neutrophil count on chemotherapy administration and toxicity in dogs with lymphoma treated with CHOP chemotherapy. Journal of Veterinary Internal Medicine, 32(1), 384–393.

National Institute for Occupational Safety and Health. (2024). NIOSH list of antineoplastic and other hazardous drugs in healthcare settings, 2024. https://www.cdc.gov/niosh/docs/2025-103/default.html

VCA Animal Hospitals. (n.d.). Toceranib phosphate. https://vcahospitals.com/know-your-pet/toceranib-phosphate

Veterinary Information Network. (n.d.). Toceranib phosphate (Palladia). Veterinary Partner. https://veterinarypartner.vin.com/default.aspx?pid=19239&catId=102894&id=4952879

This article is for educational purposes only and is not a substitute for veterinary care. It describes medication categories in general terms and deliberately does not include doses. No medication should be given to your dog without your veterinarian's direction, and human medications should never be given without veterinary advice. If your dog develops a fever following chemotherapy, is vomiting blood, cannot keep water down, or is collapsed or very weak, seek emergency veterinary care immediately.