Is It Safe To Combine Chemo, Vaccines & Other Medications?

When a patient is receiving chemotherapy a common question that the family asks is whether they can still receive their normal vaccines, allergy medications, as well as flea, tick and heartworm preventatives.

These are all VERY good questions to ask. Below I've covered different classes of medications and whether they are safe to give concurrently with chemotherapy.

Flea, Tick & Heartworm Preventative

All patients should continue on their regular flea, tick and heartworm preventatives. These medications should be given year-round. Flea, tick and heartworm prophylaxis does not interfere with chemotherapy. Instead, these medications help to keep a cancer patient free from the many tick-borne diseases that exist, heartworm disease, and the burden and discomfort of fleas.

Thyroid Supplementation

If your dog receives thyroid supplementation for hypothyroidism, you should continue this medication and continue to have your dog's thyroid levels checked regularly to ensure that a dose adjustment isn't needed. Thyroid supplementation will not interfere with chemotherapy.

Allergy Medication

Many dogs suffer from allergies and receive Benadryl, steroids, and/or Apoquel. There is no contraindication to giving Benadryl for a dog with cancer - just remind your oncologist that your dog is receiving this. In some cases, your oncologist (or family vet) may stop the steroids if they feel that your dog's cancer could benefit from an NSAID - this class of anti-inflammatory is given with many types of carcinoma. Since prednisone cannot be given with an NSAID it is VERY important for your oncologist to know if your dog is taking steroids.

What about Apoquel? If your dog is receiving Apoquel your oncologist will likely recommend that you stop giving this medication while your dog is receiving chemotherapy. In some dogs, Apoquel can reduce the white blood cell count. Since chemotherapy agents can reduce white blood cell counts as well, it's best not to combine these two medications. Instead of Apoquel, consider Cytopoint, a monthly injection for dogs with allergies (which does not affect white blood cell counts).


Studies have shown that a dog's body reacts the exact same way to a vaccine whether they are receiving chemotherapy or not. That being said, oncologists tend to be a bit conservative when it comes to vaccine recommendations during chemotherapy treatment. Many oncologists will recommend that the patient continues to receive rabies (a disease that is fatal to humans and therefore vaccinating dogs is required by law) and leptospirosis vaccines (if leptospirosis is endemic in your area) during chemotherapy treatment. There might be other geographic exceptions, so please check with your local oncologist. When chemotherapy is finished, the standard vaccines can be resumed.


Many dogs with cancer receive supplements. If your dog is receiving supplements AND is undergoing chemotherapy, be certain to check with your oncologist to ensure that the supplements will not make the chemotherapy less effective. There are MANY common supplements that will make certain chemotherapy agents less effective, so this is important. There is some evidence that the common supplement turmeric may decrease the anti-cancer activity of both doxorubicin and Cytoxan chemotherapeutics, which is very scary considering how often we rely on these medications and how commonly turmeric is being used.

A useful resource is the "About Herbs" section of the Memorial Sloan Kettering Cancer Center Integrative Medicine online portal. Check out the A-Z guide of herbs and supplements that have been used to treat cancer. The website lists the research behind their purported efficacy, any known herb-drug interactions as well as a very helpful "do not take if" section. It is the most comprehensive list I have found yet.

NSAIDS (Carprofen, Rimadyl, Meloxicam, Vetprofen)

This class of medications is the "canine safe" version of ibuprofen. These medications are commonly used to treat arthritis and pain in older dogs. If your dog is diagnosed with cancer, please tell your care provider if your dog is receiving an NSAID. There are many types of cancer that require treatment with steroids, such as prednisone. If a patient accidentally receives both prednisone and NSAIDs they could develop an ulcer, which is potentially fatal. We typically allow a 3-5 day "washout" between stopping an NSAID and starting prednisone. Your care provider might even add additional stomach protectants to decrease the likelihood of ulcer formation such as omeprazole (Prilosec AC) and sucralfate.

Medicine is never black and white and there are usually exceptions to every rule. So as a general rule, if your dog is starting NEW medications for a newly diagnosed disease, make sure that you give your veterinarian a list of all if their current medications and supplements to decrease the chance of an unfavorable reaction.

Since many veterinarians are not familiar with supplements, feel free to do your own research on a reputable website such as the Sloan Kettering "About Herbs" directory and make sure that you don't find any worrisome herb-drug combinations.

Dr. Lori Cesario

Board Certified Veterinary Oncologist

PS: I'm happy to now offer online oncology consultations. Learn more about how this service can help by visiting the Vet Cancer Consultants site.

A few other articles you might enjoy...

(1)Dog Breeds And Their Associated Cancers

(2) Mast Cell Tumors - The Great Imitator in Canine Cancer

(3) Canine Splenic Tumors - What You Need To Know

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