Is Antifreeze toxic to cats?

Ethylene glycol is metabolized into toxic byproducts that cause severe acute kidney failure and central nervous system depression.

The vet runs blood tests for ethylene glycol, other bloodwork and urine tests for crystals, and may start treatment before the diagnosis is confirmed if no reliable test is available. Testing is harder in cats: point-of-care kits can't detect levels below 20 mg/dL, which is also the lethal blood level Merck gives for cats, and ASPCApro says in-house tests are less sensitive and specific than testing at a human hospital lab. The antidote is fomepizole (4-MP) or ethanol, which block the enzyme that turns ethylene glycol into the breakdown products that damage the kidneys. Cats need a much higher, extra-label dose of fomepizole than dogs. Your cat also gets IV fluids to correct dehydration and flush ethylene glycol out in the urine, and the vet corrects acidosis, low blood sugar or low calcium as needed. Once the kidneys are failing and urine output has dropped or stopped, the antidote is of little benefit, because almost all of the ethylene glycol has already been broken down.

The outlook depends on how fast treatment starts: the longer the delay, the worse it gets. Calcium oxalate crystals in the urine signal a poor prognosis, and in cats they can appear as early as 3 hours after drinking. Once kidney failure has developed, the prognosis is guarded to poor.

• Car antifreeze and radiator coolant, the main source. The poison in them is ethylene glycol. Concentrated antifreeze can be up to about 95% ethylene glycol, and premixed 50/50 coolant is also sold.
• Spills and leaks on garage floors and driveways, leaking cars, containers kept in garages and sheds, and old coolant that was not disposed of properly. Pets lap up the puddles.
• Antifreeze tastes sweet, which tempts pets to drink it. US makers have added a bittering agent since 2012, but the Merck Veterinary Manual says some animals may still find it palatable.
• Toilets and RV plumbing winterized with antifreeze. Pet Poison Helpline sees dogs that drank from toilets in cabins.
• Some snow globes, which have been found to contain ethylene glycol. A pet that licks the liquid from a broken globe can be poisoned.
• Other products: windshield de-icers (some contain less ethylene glycol), aircraft de-icers, brake, transmission and hydraulic fluids, motor oil, and less obvious ones such as solar heating fluids, ice-rink freezing equipment, bases of portable basketball hoops, paints, solvents, wood stains, printer and pen inks, photo-developing fluids and some eye masks.
• In cats, poisoning has been reported from ethylene glycol absorbed through the skin from topical products.
• Cases peak when people add antifreeze or flush radiators. Merck says that is fall, winter and early spring in cold climates; Pet Poison Helpline names summer and winter.

• Store antifreeze in closed containers out of pets' reach, and dispose of old antifreeze properly.
• Clean up any spill or leak at once. Soak it up with cat litter, sand or sawdust, or dilute it with several gallons of water, so pets can't lick the residue.
• Choose propylene glycol-based antifreeze, sold as 'pet-safe', where you can. It has a much wider margin of safety, but it is not harmless, so keep pets away from it too.
• Keep pets away from leaking cars, from garages and sheds where coolant is kept, and from toilets or RV plumbing winterized with antifreeze.
• Keep snow globes where pets can't knock them over, and keep pets away from a broken one.
• Keep other car fluids out of reach as well, including brake and transmission fluids and windshield de-icers.