As the nights draw in and the weather gets colder, we’re all being bombarded with (very good!) advice from the motoring organisations, reminding us to top up the antifreeze in our cars. This is important, and we’re not advising against it – but you must be really, really careful with the stuff, because antifreeze is one of the commonest poisonings in cats, and has the highest fatality rate.
What is poisonous about antifreeze?
Most antifreeze formulations contain a chemical called ethylene glycol. This is a highly dangerous toxin to all animals (dogs, cats, birds, even people); however, cats are uniquely sensitive to its effects. The average lethal dose is 6.6 ml per kg body weight in a dog, but only 1.4ml in a cat. That works out as 6ml or about 1 teaspoon for a fatal dose in an average-sized cat. Most bottles of antifreeze solution sold in a supermarket or petrol station are highly concentrated, and even a small spill is likely to be dangerous.
Why is poisoning so common?
Ethylene glycol tastes very, very sweet, which explains why dogs, wildlife (and children) will drink it if given the chance. However, while cats lack the ability to taste sweetness, they are highly attracted to the taste too, so it may be that it triggers other taste buds too – although sadly, we can’t ask our cats to find out! Whatever the reason, it is highly palatable and will be drunk in preference to plain water.
What does it do?
One swallowed, ethylene glycol acts very like alcohol, causing alteration to brain pathways and then depressing the nervous system and causing severe dehydration. Like alcohol, it is broken down in the cat’s liver by an enzyme called alcohol dehydrogenase – but unlike alcohol, the enzyme converts it into even more dangerous compounds. These, especially glyoxalic acid and calcium oxalate monohydrate, damage the kidneys, causing acute kidney failure. Once the ethylene glycol has been converted into oxalates, the effects cannot be prevented – kidney damage inevitably follows.
What are the symptoms?
In the initial phase of poisoning, which may take as little as 30 minutes, you may see altered behaviour, wobbliness and difficulty balancing, rolling eyes (nystagmus), increased urination and vomiting. However, while your cat being drunk may appear amusing, it’s a sign that the toxin is starting to work.
The cat then becomes progressively more depressed and unresponsive, and may even lose consciousness (somewhat analogous to an alcoholic coma). About 12-24 hours after drinking the antifreeze, the kidneys start to shut down, producing less and less urine (oliguria), until total kidney failure (anuria) results, usually after 3-4 days.
Can it be treated?
Once the oxalates have formed, the only treatment available is supportive – intensive care, intravenous fluids etc., in the hope of limiting (but not preventing) the kidney damage.
If, however, we can see the cat before the alcohol dehydrogenase has started working, we can give an antidote. There is a drug called fomepizole which slows down the production of toxic products to the point where the body can handle their effects; sadly, it is very, very hard to get hold of.
The good news is that alcohol can also act as an antidote, by “flooding” the alcohol dehydrogenase system and slowing down the conversion of the ethylene glycol; the bad news is that alcohol is also pretty toxic to cats. As a result, NEVER try this at home, use of alcohol in a cat requires intensive care and constant monitoring at the practice!
What are my cat’s chances if they get poisoned?
If we can begin treatment within 3 hours of drinking the stuff (NOT 3 hours of symptoms appearing), the prognosis is fairly good, although they will probably require a long stay with us to recover. If it’s after that 3-hour window, many cats will not survive; and if it’s more than 12-24 hours, the vast majority of victims will die.
Is there anything I can do to keep them safe?
Make sure that cats never have access to antifreeze or, if possible, use a pet-safe antifreeze in your car. In addition, never put antifreeze in ponds or water features, or leave any spillage lying around where the cat can lap it up.