My dog ate fluorouracil – what should I do?

Updated 2026-09-30 · 2 sources

Based on: US FDA – Center for Veterinary Medicine, Pet Poison Helpline

Call a vet now

Call your vet or the nearest emergency vet right now. Signs can start within 30 minutes after ingestion.

What to do now

What to do right now

Call your vet or the nearest emergency vet.
Note what was eaten, how much, and when.
Bring the packaging.
Keep your dog calm and remove what is left.

Don't

Do not make your dog vomit unless a vet tells you to.
Do not give any human medicine.

Why it can be dangerous

5-FU is one of the most dangerous pet toxins.^[2] Signs of fluorouracil poisoning can start within 30 minutes after a pet ingests the medicine.^[1] In reports received by the FDA involving 20 dogs, all 20 dogs died.^[1]

Signs to watch for

vomiting, sometimes with blood
seizures
tremors
difficulty breathing
lethargy
drooling
diarrhea, with or without blood
incoordination

Signs can start within 30 minutes after a pet ingests the medicine.

Where it is found

prescription topical treatment for human skin cancers
actinic keratosis treatment

What the experts say

“Signs of fluorouracil poisoning can start within 30 minutes after a pet ingests the medicine”
— US FDA – Center for Veterinary Medicine [1]

If your pet is struggling to breathe, has collapsed, is having a seizure or can't stand up: go to the nearest vet now.

Not sure how serious it is?

OkPaw asks a few quick questions about your pet and tells you in 30 seconds whether it can wait. Free on Google Play for Android.

OkPaw is on Android now – an iPhone version is on its way.

Common questions

How much is dangerous?

5-FU is one of the most dangerous pet toxins.^[2]

How soon can signs start?

Signs of fluorouracil poisoning can start within 30 minutes after a pet ingests the medicine.^[1]

Where might this medicine be found?

It is a prescription anti-cancer medication used topically to treat human skin cancers and actinic keratosis.^[2]

Sources

How this page was made: written with the help of AI from the sources below, then checked claim by claim against those sources. Urgency levels follow OkPaw’s fixed safety rules. It is guidance, not a diagnosis. How we write our pages

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