Antifreeze and Pets: Ethylene Glycol, the Sweet Poison in the Garage
A small puddle under a car on a cold morning looks harmless. To an animal it can smell and taste attractive, and the amount needed to kill a cat is only a few millilitres. Antifreeze poisoning is one of the clearest cases in veterinary toxicology where hours change the outcome, and one of the clearest where owners can be reassured by a false recovery. This guide covers what ethylene glycol is, the published lethal doses, the timeline, the places it hides and what to do. It is general information from a website editor, not veterinary advice.
What is in antifreeze, and why animals drink it
The toxic ingredient is ethylene glycol. The Merck Veterinary Manual says the sweet taste of antifreeze, together with its availability and small minimum lethal dose, contributes to how often poisoning occurs. It adds that since 2012 manufacturers in the United States have added a bittering agent, but some animals may still find the product palatable. So a bittered product is not a guarantee, and older bottles in a garage may predate it. Radiator antifreeze can be up to about 95 percent ethylene glycol or sold pre-diluted as 50/50 mixes.
How little is too much
Merck gives the minimum lethal dose of undiluted ethylene glycol as 1.4 mL/kg in cats and 4.4 to 6.6 mL/kg in dogs. Using example numbers and the arithmetic written out:
- A 4 kg cat: 4 × 1.4 = 5.6 mL, a little more than a teaspoon (about 5 mL) of undiluted product.
- A 10 kg dog: 10 × 4.4 = 44 mL at the low end, up to 10 × 6.6 = 66 mL; roughly three to four tablespoons.
- A 4 kg cat and a 50/50 mix: the product has half the ethylene glycol, so roughly twice the volume, about 11 mL, is needed to reach the same dose.
These are minimum lethal doses from the manual for undiluted liquid; poisoning can still happen below them, particularly if treatment is delayed, and an animal licking a spill from paws or fur can reach meaningful amounts quickly for a small body. Merck also notes younger animals may be more susceptible. Our ethylene glycol reference lets you try other weights.
The timeline in three stages
Merck describes the course in dogs and cats:
- 30 minutes to 12 hours. The animal may look drunk: vomiting, increased thirst and urination, depression, stupor, wobbly gait and knuckling of the paws. This is caused by the ethylene glycol itself acting on the nervous system.
- A brief apparent recovery may occur around 12 hours. The pet may look better, eat and move more normally. This is the dangerous false reassurance.
- Kidney failure. In cats, oliguric (low urine output) kidney failure begins at 12 to 24 hours and progresses toward anuria (no urine). In dogs it begins at 36 to 72 hours. Later signs include painful, enlarged kidneys, lethargy, possible seizures and coma.
The reason for the kidney phase is that the body converts ethylene glycol into more harmful breakdown products, and those damage the kidneys. A treatment that works against that conversion, which Merck names as fomepizole or ethanol, must be started early, before the damage is done. Merck states that treatment requires early intervention. We do not give doses, because only a vet can decide these; the point for an owner is that the window for the best treatment is hours, not days. If you leave it until the animal is clearly in kidney failure, options narrow sharply.
Where ethylene glycol hides
Merck lists these sources:
- Vehicle radiator antifreeze and coolant, including spills and drips on driveways and garage floors, and discarded containers.
- Other automotive and household products, and some brake and transmission fluids.
- Heat-exchange fluids in solar collectors.
- Ice-rink freezing equipment.
- Topical products, which can poison cats through skin absorption.
To that list we would add things that hold liquid: open buckets under cars, drain pans from fluid changes, and leaking radiators on parked vehicles. Windscreen wash and de-icer products vary in composition, so read the label rather than assuming. Some antifreeze products are marketed as safer for pets and use propylene glycol instead; that is a different chemical, but "pet-safe" labelling should not make you careless, and ask a helpline if you are unsure about a product.
Signs to watch for, and why they are unreliable
Stage-one signs resemble alcohol intoxication, which means they can be mistaken for something else, such as a head injury, a stroke or a stomach bug. Excess drinking and urination are easily missed in a cat that uses a litter tray. If you suspect antifreeze, do not rely on a symptom checklist: call immediately. If the pet has already had an apparent recovery, treat it as possible stage two; do not relax. Laboratory tests at a vet can check for ethylene glycol or its effects, but the test is best done early, and a vet may begin treatment on suspicion.
What to do
- Stop access. Move the pet away from the spill, wipe up the liquid with disposable towels, rinse the area and bin the towels in a sealed bag so other animals cannot reach them.
- Note what was spilled (brand and concentration), how much might be missing, the time, and your pet's weight.
- Call a vet or poison service immediately, even if the pet seems fine. Go to a clinic straight away rather than waiting for symptoms; phone while travelling and take the container.
- Do not induce vomiting unless a vet instructs you to; see our first-hour guide.
- Tell the vet about any possible exposure of other animals in the household. If antifreeze was open, another pet may have been drinking too.
If you only suspect your cat licked a puddle in the road or a neighbour's drive, the same rule applies. The cost of a precautionary call is small, and the margin for error in cats is tiny.
Why cats and small animals are hit hardest
The lethal dose scales with body weight, so a cat's few millilitres is a tiny amount of liquid: a lick of a puddle, a paw dipped in a spill and then groomed, or a drink from an open container. Merck notes cats can also be poisoned through topical products that contain ethylene glycol. Cats additionally show kidney failure sooner than dogs (12 to 24 hours against 36 to 72), leaving less time to react. A free-roaming cat may drink in a neighbour's driveway without you ever knowing, so unexplained drunken behaviour in a cat in cold weather deserves a call to the vet at once. Dogs are no safer for being larger; a dog that laps a spill from a drain pan can easily reach the 4.4 mL/kg lower figure, because undiluted fluid is concentrated.
A scenario to rehearse
You find a 3.5 kg cat unsteady in the garage, next to a dripping radiator hose and a shallow puddle. You do not know if it drank. The sequence is simple: lift the cat out, towel up the puddle, photograph the bottle and the leak, and phone the nearest 24-hour vet while you put the cat in a carrier. The vet may start treatment on suspicion, and the sooner it begins the better, since the stage-three kidney damage Merck describes is the part that is hard to reverse. For this cat, the minimum lethal dose is about 3.5 × 1.4 = 4.9 mL of undiluted product. That is a mouthful. Do not spend the first hour searching the internet; spend it travelling.
What a vet visit looks like
Because the details of treatment belong to the clinic, this is only an outline. Expect questions about the product, the time, and the animal's weight. The vet may examine the pet, run blood and urine tests to look at kidney function and acid-base balance, and start the specific early treatment Merck mentions if poisoning is suspected or confirmed. Hospital stays can be several days, with repeat testing of kidney values. Even after apparent recovery, follow-up testing is common. If you have the container, the clinic can check the concentration and work out how much your animal could have taken, which helps decide how aggressive the response needs to be. If the exposure is uncertain, be honest about it; vets would rather treat a possible case than miss a real one.
Prevention
Store antifreeze in a sealed, labelled container on a high shelf, and never decant it into a drink bottle. Clean up spills fully and fix leaking radiators. When topping up or draining a radiator, work on a hard surface where you can catch and dispose of drips, and keep animals out of the garage during the job. Take used coolant to a recycling facility. Consider asking neighbours who service vehicles on the street to do the same, especially if your cat roams. Keep the numbers below near the garage door as well as on your phone. Our pet-proofing checklist covers the garage and shed, and the rodenticide guide covers another thing that should not be on the garage floor.
If your pet may have had antifreeze
This article is general information, not veterinary advice. Call a vet or poison service immediately: ASPCA Animal Poison Control +1 888-426-4435, Pet Poison Helpline +1 855-764-7661 (fees may apply), or in the UK your own vet or the Animal PoisonLine on 01202 509000 (charges may apply). Because treatment works best early, go to an emergency vet as soon as you can.
Sources
- Merck Veterinary Manual: Ethylene glycol toxicosis in animals
- Merck Veterinary Manual: Overview of ethylene glycol toxicity
- ASPCA Animal Poison Control: What to do if your pet is poisoned
- PDSA: Animal PoisonLine
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Not veterinary advice. The authors are not veterinarians. If your pet may have eaten something toxic, call your vet or a pet poison line now: ASPCA Animal Poison Control (US) +1 888-426-4435, Pet Poison Helpline (US/Canada) +1 855-764-7661, Animal PoisonLine (UK) 01202 509000. Fees may apply. Spotted a mistake? Email huhuwen09@gmail.com with the page address and we will check and correct it.