Until 1996, almost no data existed on the incidence of ethylene glycol (antifreeze) poisoning. In that year, the American Society for the Prevention of Cruelty to Animals, in co-operation with Safe Brands Corp., undertook a survey of American veterinarians to ascertain how many dogs and cats had been treated for accidental ethylene glycol poisoning in the preceding 12 months in the United States, and of these, how many had died. A conservative figure was 118,000 dogs and cats, with 91,000 of them dying. Veterinarians suspect that this may only be half the actual number of cats and dogs affected. And this survey does not even look at the incidence in wild animals.
Toxicity of ethylene glycol
As little as one teaspoon of ethylene glycol can kill a small dog or a cat, while one tablespoon can kill a large dog. Since conventional antifreeze contains 95% ethylene glycol, it truly is a highly toxic substance. Even when diluted 50% with water and placed in a car radiator, two teaspoons will kill a small dog or a cat, and two tablespoons (two ounces) a large dog. Cats are particularly vulnerable to drips and leaks under vehicles where they like to sit. Given that ethylene glycol is attractive to animals because of its sweet flavor, it is frightening to consider the consequences.
Safe handling practices
Ensure that your vehicle is in good working order, and that the cooling system has no leaks. Should the system overheat, leak, overflow, or break down, clean up any spills immediately and thoroughly. Store opened antifreeze in sealed, labeled containers and keep it off the floor away from animals. Used antifreeze as well as empty containers should be disposed of at your local hazardous waste depot.
Signs, treatment and prevention
Any of the following signs can be seen over a period of 12 hours or several days: excessive thirst and urination (within the first hour), lack of coordination (almost as if the animal were drunk), weakness, nausea, vomiting, diarrhea, tremors, rapid breathing and heart rate, convulsions or paralysis.
It takes between 12 and 24 hours for ethylene glycol to be completely metabolized into the acid which damages the kidneys. It is usually felt that medical treatment during the first 12 hours has some hope of success, much more remote during the second 12 hours, and after 24 hours, there is little chance of recovery. The animal will go into total renal failure, and usually there is too much permanent damage done to the kidneys to reverse it.
A new drug, Antizol-vet (approved in the U.S.A. but not in Canada), provides a 36-hour window of opportunity for improving the chances of saving animals. Haemodialysis, an expensive treatment for dogs, is currently available in some locations in the U.S.A. Success rates are only about 50% and depend on how much damage the kidneys have sustained.
With such a poor prognosis in a majority of cases, prevention both in terms of safe handling of antifreeze and watching out for your animal is the best approach. If you suspect he has ingested antifreeze, take him immediately to the veterinarian.
Alternatives to conventional antifreeze
Propylene glycol antifreeze, which is slightly less than half as toxic as ethylene glycol antifreeze, and not attractively sweet for animals, has been developed and improved over the last 10 to 15 years. Currently, propylene glycol antifreeze coolant is more widely used in South America and countries in continental Europe than in North America. It is more expensive than ethylene glycol, but it can now be used in aluminum engine blocks. It is effective in extremely cold temperatures (25-66 Fahrenheit degrees below zero), if a higher ratio of antifreeze to water is used.
Two propylene glycol antifreezes are available: Sierra by Old World Industries in the U.S.A. and Prestone Low Tox in Canada. The chemical companies claim that propylene glycol is already earmarked for other products and that there is not enough propylene glycol to replace ethylene glycol in antifreeze. It would require a major shift in production: retooling plants or building new plants, while ethylene glycol factories would lie idle. For the most part, both kinds of antifreeze are made by the same chemical companies and it appears that they have a vested interest in maintaining the status quo, allowing propylene glycol antifreeze only a niche market.
It is unclear why the major car manufacturers have so far refused to put propylene glycol in their new vehicles. The price differential – about $1.00-2.00 more per car – appears to be the only reason. Would car buyers not be willing to pay this additional, small amount if given the option?
In the early 1990s, Bitrex (denatonium benzoate) was added to ethylene glycol antifreeze as a taste inhibitor. Conflicting reports of the reasons for its falling into disuse have been given: some felt that it lost its bitterness after use in a radiator, and others questioned whether animals actually found it unpalatable.