Antifreeze
- Mary Malucci
- Jun 28, 2023
- 3 min read
Updated: Jan 29, 2025
When I first started working in veterinary medicine, all antifreeze products were made with ethylene glycol. Ethylene glycol is highly toxic, even small amounts ingested can lead to death. Many pets find it appealing because of its sweet taste. It is rapidly absorbed in the GI tract, metabolizing into harmful compounds that severely damage the kidneys, causing them to fail.
As antifreeze manufacturers became more aware of ethylene glycol's toxicity, they began to use propylene glycol as their active ingredient instead. Although these two compounds are related, propylene glycol is considered GRAS or generally recognized as safe. It is used in trace amounts in a wide variety of products including certain medicines, cosmetics, dog foods and human foods. For most humans, the trace amounts used in human products don't seem to cause any health issues. Recent controversies regarding propylene glycol in pet foods arise from the fact that propylene glycol will accumulate in our pet's bodies if the food they eat every day contains it. Propylene glycol is used to retain moisture in semi-moist foods. Studies have shown that low-level chronic ingestion of propylene glycol will cause cats to develop a specific form of anemia called Heinz body anemia. Consequently, the FDA has prohibited its use in commercial cat foods. Anecdotal evidence suggests that dogs may suffer adverse effects from chronic propylene glycol ingestion but, as of this writing, no specific studies have been performed.
In concentrated forms like antifreeze, propylene glycol can still make our pets very sick. It takes a larger volume of propylene glycol antifreeze to cause toxicity, about 9 mls per kg, compared to the very small volume of ethylene glycol antifreeze required to cause toxicity and death, about 1.4 mls per kg for a cat. The initial symptoms of propylene glycol poisoning will mimic ethylene glycol toxicity. Both products will cause acute renal failure at lethal doses.
Ethylene glycol poisoning is divided into three stages.
Stage 1 occurs between 30 minutes and 12 hours after ingestion. People often describe these pets as appearing drunk. They become uncoordinated and lethargic and begin drooling and vomiting. Some of these pets will drink excessive amounts of water and urinate large volumes. Higher doses may lower body temperature and cause seizures and coma.
In Stage 2, the symptoms seen in Stage 1 fade away, causing many pet owners to think their pet is getting better. Unfortunately, the ethylene glycol is quietly continuing to damage the kidneys. Signs like dehydration and elevated heart and respiratory rates may be seen. Stage 2 occurs between 12-24 hours after a pet ingests antifreeze.
Stage 3 is marked by severe and irreversible kidney damage. When ethylene glycol breaks down in our pet's bodies, calcium oxalate crystals form and lodge in the renal tubules, causing lasting damage. Many of the symptoms seen in Stage 1 will reappear.
Treatment for both types of poisonings require hospitalization with IV fluid support and symptomatic treatments. There is a specific antidote for ethylene glycol called fomepizole but it must be administered within 3 hours of ingestion to be effective. There is no specific antidote for propylene glycol. Ethylene glycol screening tests are not always definitive because propylene glycol is closely related to ethylene glycol and will result in false positives.
My experience with treating ethylene glycol poisoning cases is that pets who arrive at the ER already symptomatic have a very poor prognosis and most of them die regardless of treatment. While propylene glycol may be safe enough in trace amounts, its equally as dangerous to our pets in concentrated forms like antifreeze.
The best way to protect our pets is to keep the antifreeze inaccessible. If you like to maintain your own car, be sure to clean up thoroughly when changing the antifreeze. Keep the container tightly sealed and out of reach. Clean up spills immediately and dispose of contaminated rags in a sealed container. If the spill is large enough to require an absorbent like kitty litter, be sure to dispose of contaminated absorbent in sealed containers. Prohibit access underneath vehicles. Keep pets away from outside water sources that may be contaminated.
Other products containing high concentrations of propylene glycol include artificial smoke, ink, liquid pharmaceutical medications, PVC products and deicers. For more information about ethylene glycol and propylene glycol, consult the following articles.
"Ethylene Glycol Toxicosis in Animals"
"Propylene Poisoning in Dogs"
"Propylene Glycol: Educate yourself and your veterinary clients"
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