Antifreeze Poisoning in Dogs: Signs, Risks, and Prevention

Ethylene glycol is the active ingredient in most automotive antifreeze. It is a sweet-tasting, odorless liquid that dogs may be attracted to and voluntarily drink³. It has a very narrow margin of safety, which means a tiny amount can result in severe poisoning³. The Merck Veterinary Manual reports that the minimum lethal dose of undiluted ethylene glycol in dogs is very small¹. The pet-owner edition of the Merck Manual puts that in everyday terms: only a small amount can be lethal for a dog².

Ethylene glycol is not limited to radiator coolant. The ASPCA Animal Poison Control Center lists other places it can turn up: the base of portable basketball hoops, toilets winterized to prevent freezing, printer and pen inks, snow globes, and some household latex paints⁵. VCA Animal Hospitals adds hydraulic brake fluid, motor oils, solvents, wood stains, and film processing solutions³. The AKC notes it can also appear in some windshield de-icers and cosmetics, although in lower amounts⁴.

Since 2012, antifreeze manufacturers in the United States have added a bittering agent to deter ingestion, but the products may still be palatable to some animals¹.

Ethylene glycol poisoning is most common in temperate and cold climates, because antifreeze is used to both lower the freezing point and raise the boiling point of radiator fluid². In colder areas, cases are seasonal, with most occurring in the fall, winter, and early spring, when antifreeze is added to radiators or cooling systems are flushed¹. A puddle of coolant under a car in a driveway or parking lot can look inviting to a curious dog.

Clinical signs depend on how much was ingested and how much time has passed. Veterinary sources describe the progression in stages¹⁴:

• Stage 1 (30 minutes to 12 hours): Signs resemble alcohol intoxication. Dogs may vomit, stumble, seem depressed or lethargic, drink more than usual, and urinate more¹⁴. The ASPCA also lists unsteadiness on the feet and loss of appetite⁵. Some dogs may have seizures or a low body temperature⁴.
• Stage 2 (12 to 24 hours): Dogs may appear to improve. But this apparent recovery is misleading. Internal damage is progressing, with dehydration and increasing heart and breathing rates²⁴.
• Stage 3 (36 to 72 hours in dogs): Severe kidney failure develops. The kidneys become swollen and painful. Dogs produce little or no urine, stop eating, vomit, and may have mouth ulcers, drooling, rapid breathing, seizures, or coma¹²⁴.

VCA warns that a delay in treatment usually results in death, and the prognosis is very poor once clinical signs have developed³.

Time is critical. The Merck Veterinary Manual states that an antidote is available for dogs, but it is only effective if given before kidney failure develops². The AKC Chief Veterinarian warns that dogs must be treated within 8 to 12 hours after consuming antifreeze, or the antidote will be ineffective⁴. Left untreated, ingestion of ethylene glycol is fatal⁴.

Contact your veterinarian or an emergency veterinary clinic right away. The ASPCA recommends bringing the antifreeze packaging with you, so the veterinarian can determine the best treatment based on the amount ingested and the product ingredients⁵. Do not try to make your dog vomit without professional guidance, because vomit can be a choking hazard if your dog is showing neurological signs such as staggering⁴.

At the clinic, veterinarians may use blood tests to measure ethylene glycol levels, along with other blood work and urinalysis³⁴. Treatment includes an antidote (fomepizole or ethanol), intensive intravenous fluids, and supportive care to manage nausea, electrolytes, and blood pH¹⁴.

Prevention is straightforward and effective:

• Switch to pet-safe antifreeze. Products that contain propylene glycol instead of ethylene glycol are available. Propylene glycol has a much wider margin of safety and does not have the sweet taste that attracts animals²⁴⁵.
• Store antifreeze securely. Keep containers sealed and out of reach. Dispose of old antifreeze through a household hazardous waste program⁴.
• Clean up spills immediately. The Merck Veterinary Manual recommends covering any residue with cat litter, sawdust, or another absorbent material to discourage pets from licking it up².
• Check for leaks. Look under your car regularly for coolant drips in garages and driveways⁴.
• Watch for hidden sources. If antifreeze is used in toilets to winterize plumbing, keep the lid down and the door closed⁴⁵.
• Keep poison control numbers handy. The ASPCA Animal Poison Control Center (888-426-4435) and Pet Poison Helpline (800-213-6680) are available around the clock⁴⁵.

The bittering agent added to antifreeze since 2012 may reduce voluntary ingestion, but there is limited published data on how well it works in practice¹. Propylene glycol antifreeze is less toxic than ethylene glycol, but it is not completely risk-free; the Merck Veterinary Manual notes it can still cause a similar syndrome, though the outlook is usually better². The exact amount that will cause harm in a given dog depends on body weight, the concentration of the product, and how quickly treatment begins.