Antifreeze Poisoning: What Happens in the Dog’s Body

by Jennifer Coates, DVM

Most dog owners are aware that antifreeze containing ethylene glycol (EG) is dangerous stuff. 

But, do you know exactly how it wreaks havoc in a dog’s body? 

I didn’t think so (I had to look up a few of the finer points too). Let’s review how ethylene glycol is absorbed, metabolized, and excreted from the body. The information is essential to understanding why antifreeze poisoning has to be treated so quickly.

It does not take much antifreeze to make dogs REALLY sick. 

The minimum lethal dose of ethylene glycol is 2-3 ml/lb. In other words, less than 2 fluid ounces can kill a 20 pound dog.

So I’m going to invent a 20 pound dog. His name is Rascal, and he just found a puddle of sweet-smelling liquid underneath his neighbor’s leaky old car (someone left his backyard gate open, but he stays close to home). He tastes it and thinks, “Not bad” and proceeds to lap up the rest of the antifreeze… you guessed it, about two ounces worth.

Before his owners even realize he’s out of the yard, the ethylene glycol is being absorbed into his bloodstream. 

He wanders home, is let inside, and within just a few hours starts acting a little funny. He’s very thirsty but dull and depressed, and when he tries to walk he looks like he’s drunk… stumbling and swaying from side to side. This occurs because EG can easily cross into the cerebrospinal fluid that bathes the brain and once there, has an adverse effect on neurological function.

Now our tale can go in one of two ways:

1. Rascal’s owners think, “Uh oh, he was just out of the yard and now he’s not right. Let’s get him to the vet’s ASAP” or
2. “Huh, isn’t that funny. I bet he’ll feel better in the morning.”

Let’s make #1 our best case scenario. 

Rascal’s owners bring him in, mention that he’s been roaming the neighborhood, and based on this history and Racal’s clinical signs the vet thinks of the possibility of antifreeze poisoning. The bench-top test comes back positive, and Rascal is immediately given activated charcoal, put on intravenous fluid therapy, and treated with either a diluted ethanol solution or fomepizole, either of which will compete with one of the enzymes needed to convert EG into its toxic metabolites as long as it is given within eight hours of ingestion. After several days of hospitalization, treatment, and close monitoring, Rascal is sent home and recovers uneventfully.

Now on to scenario 2:

As the hours pass (12-24) without diagnosis or treatment, Rascal’s liver starts to metabolize the ethylene glycol, first into glycoaldehyde, then glycolic acid, and finally glyoxylic acid, which makes the body more acidic than normal.

Rather than getting better, he now is breathing heavily, is coughing a little, and his heart is racing.

Approximately 24 hours after exposure, Rascal is starting to break down the glyoxylic acid that has formed, creating oxalic acid that combines with calcium to form calcium oxalate crystals (and low blood calcium levels). The calcium oxalate crystals travel through his bloodstream and become lodged in and severely damage his kidneys. Rascal wants to drink a lot of water but is urinating out all he takes in. As more and more damage accrues (24-72hrs), Rascal has so little kidney function left that substances like blood urea nitrogen and creatinine accumulate in his blood stream, he no longer produces much if any urine, his mouth becomes ulcerated, he starts having seizures, and he will die without dialysis and a kidney transplant.

Don’t let your dogs be victims of scenario two. 

Bring them to the veterinarian immediately if you ever have reason to suspect they have ingested antifreeze.

***

Jennifer Coates, DVM graduated with honors from the Virginia-Maryland Regional College of Veterinary Medicine in 1999.  In the years since, she has practiced veterinary medicine in Virginia, Wyoming, and Colorado.  She is the author of several books about veterinary medicine and animal care, including the Dictionary of Veterinary Terms: Vet-speak Deciphered for the Non-veterinarian. 

Dr. Coates has recently joined the PetMD team and she is now writing for the Fully Vetted column; great blog, do check it out.

Jennifer also writes short stories that focus on the strength and importance of the human-animal bond and freelance articles relating to a variety of animal care and veterinary topics.  Dr. Coates lives in Fort Collins, Colorado with her husband, daughter, and pets.


Articles by Dr. Coates:
Kidney Disease – Say What? 
What Happens In The Dog's Body When The Kidneys Fail To Function Properly? 
Heat Stroke: What Happens In The Dog's Body?  
The Perplexities of Pancreatitis
The Other Side Of The Coin: The Cost Of Defensive Medicine
To Neuter Or Not To Neuter… That Is The Question
Don’t Forget the Physical Therapy
Common Misdiagnoses (Part 1)
Common Misdiagnoses (Part 2)
Picking the Right Dog to Breed
When Is It An Emergency?
Dog Allergies: Common, Commonly Misdiagnosed, or Both? 
Why Does The Spleen Get No Respect?
Protect Your Dog From Snake Bites 
More Creepy Crawlies
Why I Dislike Inflammatory Bowel Disease
Salmonella – A Significant Problem, Or Not? 

Related articles:
AntiFreeze Isn't Just A Winter Hazzard

Further reading:
The Basics of Antifreeze Poisoning in Pets
Treating and Preventing Antifreeze Poisoning in Pets
How to poison proof your garage