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Ask a Vet: Just How Toxic is Antifreeze for Dogs?

Dogs who consume ethylene glycol face grave danger, but recent developments have helped reduce canine fatalities from antifreeze.

 |  Feb 18th 2014  |   4 Contributions


If you live outside of the tropics and you need to travel more than a few miles, you owe a debt of gratitude to antifreeze. Without the stuff it would be nearly impossible to drive in winter.

Alas, although antifreeze makes modern winter life possible, it has a downside: It's toxic to most mammals, including dogs.

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Your vet may be able to diagnose a collapsed trachea without X-rays. (Photo of Dr. Eric Barchas by Liz Acosta)

The bad news

The most commonly used ingredient in antifreeze is called ethylene glycol. It is toxic to dogs and cats. Compounding the problem is the fact that antifreeze tastes sweet. Dogs are therefore attracted to antifreeze products containing ethylene glycol, and are prone to consuming large quantities of such products when they are available. (Cats, fortunately, aren't drawn to sweet things and are therefore less likely to consume ethylene glycol, which is good since they're especially sensitive to the toxic effects of it.)

Radiator leaks are the most common way that dogs gain access to antifreeze, but they also have been known to chew through unopened bottles of the stuff in order to consume it.

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Two dogs in an old truck by Shutterstock.

Ethylene glycol is chemically similar to ethanol, also known as the alcohol found in adult beverages. The initial symptoms of ethylene glycol toxicity are similar to those of ethanol toxicity. Dogs act drunk. They become disoriented and ataxic (which is a fancy way to say they stagger around). Vomiting may occur. Other symptoms might include increased thirst and a propensity towards somnolence (passing out).

Alcohol dehydrogenase, the enzyme in the liver that metabolizes ethanol and causes partygoers eventually to sober up, also metabolizes ethylene glycol. It is when this happens that things really head south. The metabolic products of ethylene glycol are the ones that can be fatal. They cause severe physiological derangement, which can trigger seizures, coma, and respiratory arrest. But the most lethal products of antifreeze metabolism cause a type of crystal, called calcium oxalate, to form in the kidneys. These crystals clog the kidneys, leading to kidney failure, which is fatal without lifetime dialysis (or potentially kidney transplant). Dogs exposed to large doses of ethylene glycol that do not receive treatment within five to eight hours generally have grave prognoses.

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A Labrador Retriever in a vet clinic by Shutterstock.

The good news

If caught early enough, ethylene glycol toxicity is treatable. The key to treatment is to block alcohol dehydrogenase, the liver enzyme that converts ethylene glycol into the really toxic products, from doing its work. There is a specific treatment, called fomepizole (also known as Antizol-Vet) that is highly effective in doing this. Early intervention with fomepizole generally leads to excellent outcomes.

Wait -- more bad news

Fomepizole is expensive and hard to come by. Many vets don't have access to it, or won't have it in stock when it is needed.

But more good news (sort of)

There is an alternative to fomepizole. Good old-fashioned ethanol also can occupy alcohol dehydrogenase and prevent the conversion of ethylene glycol into the super toxic products. Most vets outside of Utah and Saudi Arabia have ready access to this product.

The treatment process is as follows: Dogs are hospitalized for several days of vodka mainlining. They must be kept staggering drunk the whole time in order to keep the alcohol dehydrogenase enzymes too preoccupied to deal with the ethylene glycol. Once the ethylene glycol has cleared out of the system (the kidneys remove it, and it's not especially toxic to them unless alcohol dehydrogenase gets to it first), the vodka drip can be discontinued. One can only marvel at the magnitude of the hangovers dogs must experience after such medically induced benders.

The best news of all

Around a decade ago a state legislator in California held a contest entitled, "There Ought to Be a Law." Although I generally think we'd all be better off with fewer laws and not more of them, one entry to the contest was really good. A school child suggested that antifreeze in California should be made to taste bitter in order to discourage its consumption by pets. The entry won, and eventually became law. Cases of ethylene glycol toxicity plummeted in California.

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Yuck! A dog expressing a bad taste by Shutterstock.

In many parts of the U.S., dogs don't enjoy the nearly human status that many Californians give them. However, there is another group of individuals that can rival dogs for their ability to inflict self harm through ridiculously silly behavior. I'm talking about children. Ethylene glycol is toxic to them, too. And, as you may be aware, children like sweet things. Ethylene glycol exposure historically has been not uncommon in children.

This fact, combined with the threat that antifreeze poses to dogs and cats, inspired broader action. Many states followed California's lead in the bittering department. But most importantly, in December 2012, all US antifreeze manufacturers agreed "voluntarily" (under threat of federal action) to add bittering agents to antifreeze. Antifreeze manufactured since that time is much less attractive to dogs (and cats and kids).

This does not, however, completely eliminate the threat. There is still plenty of old antifreeze out there without bittering agents, and antifreeze produced in other countries can still be attractive to pets (for instance, in southern California many people try to save money by having their cars serviced in Mexico -- these cars likely come back across the border filled with the old, dangerous antifreeze). Dogs should not be allowed access to antifreeze under any circumstances. Keep bottles of the stuff locked up. And, since radiator leaks are unpredictable, don't leave your dog unattended in the garage.

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