Antifreeze Poisoning In Your Dog Or Cat

And Other Products That Contain Ethylene or Diethylene Glycol

Ron Hines DVM PhD

Ethylene Glycol can result in kidney failure   

Another toxic product, Xylitol   

    Grape Poisoning In Dogs + Tartaric Acid?

It is now illegal to sell non-bittered antifreeze in the USA. That does not mean that all non-bittered antifreeze is always off the shelf or not lying around in somebody’s garage, yard or places where automobiles are stored and serviced. So remain cautious with your pets. 

Please don’t confuse toxic ethylene glycol with the common food additive, propylene glycol. Propylene glycol, as it is generally used is safe. However, in cats substantial amounts of propylene glycol are toxic as well. (read here)

Since 1927, when Prestone™  first popularized non-alcohol automotive radiator coolants, ethylene glycol (EG), its active ingredient, has been the most common cause of serious accidental poisoning of dogs and cats and a serious one in children as well.

Over the years, ethylene glycol and rodent baits have accounted for about equal numbers of cases; but while most pets that eat rat or mouse poison survive, most that consume substantial amounts of ethylene glycol products do not. That is because the symptoms of rodent bait consumption are quite distinctive and veterinarians have very effective antidotes for these (Warfarin™-like anticoagulant) products that can be given after the bait was consumed.

But the early signs of ethylene glycol poisoning are vague and non-specific. So, it is very hard for veterinarians to reach the diagnosis within the 3-8 hour window when antidotes would help your pet most. After that, when a substantial amount of ethylene glycol was consumed, irreversible damage to your pet’s kidneys has most likely occurred.

There are many chemicals in the group called alcohols. Some can be safely consumed and some can not. Ethylene glycol is also an alcohol. Unlike ethanol (grain alcohol), ethylene glycol breaks down in the body to form very toxic byproducts. Because it doesn’t boil off at car radiator temperatures, it makes an ideal radiator antifreeze. It is sometimes also a constituent of brake and hydraulic fluids.

Ethylene glycol is an ingredient in certain liquid rust inhibitors. It is incorporated in solar collectors and used in many chemical manufacturing processes. I have read that it is, or was, an ingredient in the liquid placed inside decorative “snow scene” glass globes. You can read more about the places that use it and products that might contain ethylene glycol in this Wikipedia article.

Despite its wide use in a multitude of products, the most common source to pets is car antifreeze. Antifreeze poisoning occurs even in warm climates because radiator coolant in all climates contains ethylene glycol to inhibit rust and motor corrosion.

Diethylene Glycol

Diethylene glycol (DEG)is another chemical that is potentially toxic to your dog or cat’s kidneys. Diethylene glycol is a compound that consists of two joined ethylene glycol molecules. It is widely used in the manufacture of plastics and printing ink, solvents and resins. It would be most likely to be found in your home in household cleaners. 

Although both EG and DEG cause kidney damage, the method by which DEG does so is less well understood. It doesn’t appear to be the same as that of ethylene glycol (EG causes oxalate crystals to form in your pet’s kidneys). There have been occasional reported cases of poisoning in dogs due to the ingestion of this compound. (read here

Why Is Ethylene Glycol / Antifreeze So Poisonous to Pets and Humans?

Ethylene glycol is a syrupy liquid with no color, no odor and a taste that is described as somewhat sweet. The poisonous nature of these compounds were not discovered until the 1930s. That was through a tragic accident that eventually lead to the formation of the FDA. It is known as the Massengill incident.

Ethylene glycol kills in a very indirect way. The compound in its original form is not poisonous. Initially, your pet will just act tipsy –  like it would if it consumed bourbon whiskey. But a particular liver enzyme, alcohol dehydrogenase begins a process that results in a very dangerous ethylene glycol byproduct, glycolic acid. Glycolic acid is then transformed into oxalic acid. Oxalic acid combines with the calcium in your pet’s blood stream to form calcium oxalate which blocks and destroys an essential part of your pet’s kidneys, its nephrons. It does so through simple mechanical blockage and increased back pressure  (=hydronephrosis).

The breakdown products of ethylene glycol are all acidic. It is this abnormal blood acidity that is responsible for many of the early signs of ethylene glycol poisoning. If the pet survives these initial symptoms – and most do – it is the formation of calcium oxalate in its kidneys that is its chief danger. Although ethylene glycol is toxic to all animals, it may not affect them all equally because the liver alcohol dehydrogenases of different species apparently differ in their ability to begin this toxic process.

How Common Is Antifreeze Poisoning In Dogs And Cats?

That question is difficult to answer. That is because veterinarians suspect that the majority of cases in pets probably go unnoticed and unreported. Older pets that develop kidney failure are often assumed to have died of some other disease. Only on rare occasions are the kidneys of deceased pets that diet unexpectedly, examined by pathologists for the tell-tale oxalate crystals that indicate antifreeze consumption. Besides that, oxalate crystals sometimes form spontaneously in urinary tracts of dogs and cats. Read about that in cats here and dogs here

Between 1979 and 1986, 104 dogs and cats were brought to the Veterinary Teaching Hospital at Colorado State University for suspected poisoning. Of those, 30 had consumed ethylene glycol and 53 had eaten rat poison. Although ethylene glycol poisoning was not the most common problem, it was the most common cause of poisoning death. 

There is probably also a large group of pets that consume antifreeze, but not in quantities sufficient to become suddenly ill. Those pets can go on to develop kidney failure much later in life. You can read about one reported case like that here.

Do Dogs And Cats Actually Seek Out And Consume Antifreeze Because Of Its Pleasant Taste?

That is unclear and possibly untrue. Although that statement often appears on the internet and in articles about antifreeze poisoning in dogs and cats, I only know of two studies in which dogs were offered their choice of antifreeze or water. In the first study, the animals were given a choices antifreeze, straight ethylene glycol, water or sugar water. In that study, the majority of pets were very reluctant (91% of them) to drink antifreeze when ordinary tap water was available to them. That study was not very scientific, and no mention is made whether the antifreeze used might have contained bittering agents (e.g. denatonium benzoate) that were in occasional use at the time.  In the second study, neither dogs nor rats ever preferred antifreeze to water. You can read that study here.

Have You Personally Dealt With This Problem?


I saw my first case of antifreeze poisoning soon after completing veterinary school. It was a little dog that just didn’t seem right to its owners. When I examined the pet, the only thing I could find that was wrong was some tummy sensitivity in the area of its kidneys and an empty stomach. Unfortunately, the lab work showed that irreversible damage to the pet’s kidneys had already occurred. That dog did not survive. My second case of antifreeze poisons was much luckier. This was a 9-week-old Christmas-gift Labrador puppy that was seen drinking antifreeze that very Christmas day. I sent one of my staff to the neighborhood liquor store and had them purchased a fifth of vodka. I added some of that and bicarbonate to oral and subcutaneous fluids and kept the puppy drunk for 72 hours. He recovered completely. That grain alcohol is an antidote to ethylene glycol was discovered by a perceptive physician many years ago. That physician, working in Boston, treated sixteen teenagers who had mistaken antifreeze for liquor while partying in a garage. He noticed that the ones who were the drunkest were the ones who survived. 

What Might Be The Symptoms Of Antifreeze / Ethylene Glycol Poisoning In My Dog or Cat?

The first signs that a pet has consumed a substantial amount of ethylene glycol are the same as they would be if the pet had drunk an equivalent amount of grain alcohol in liquor. However, since something like bourbon whiskey is only 40-80% ethanol alcohol and antifreeze is 80-95% ethylene glycol, it will not take as much of the latter. So, the pet might act ‘tipsy” (inebriated) or it might just become inactive. It takes about 3 hours for EG to be fully absorbed from your dog or cat’s digestive system.

That initial phase continues for about six hours. Eventually, this tipsy behavior will subside, and it will appear that the problem is over. It is not, however, because the ethylene glycol has entered the pet’s liver and kidneys where it is being oxidized into toxic products that acidify the blood and begin to destroy renal tubular cells in the pet’s kidneys.

In the second phase of this problem, the breakdown products of EG (glycolic acid, formic acid, oxalic acid, lactic acid) begin to acidify the pet’s blood too much. This causes respiratory problems, changes in heart rate and nerve function. Any bodily process that is affected by your acid-base (pH balance) will be affected negatively.

These first two phases are often missed by pet owners or attributed to other things by veterinarians because they are so non-specific and variable. Perhaps you would think that your pet was “just having a bad day”. Veterinarians see hundreds of pets with similar non-specific signs every week and over 99% of them have not consumed ethylene glycol.

Very few pets will consume enough ethylene glycol to die during the first two stages. It is the third stage that is the most dangerous and unexpected to owners because it occurs without visible symptoms of distress. The glycolic acid liberated from ethylene glycol is, in itself, probably damaging to its body (directly toxic). But as your pet metabolizes ethylene glycol, this glycolic acid is further broken down into excessive amounts of oxalic acid. That oxalic acid has an affinity for (binds to) the calcium in your pet’s blood. The two combine to form excessive amounts of calcium oxalate crystals. Calcium oxalate is insoluble at body acidity – so it forms plugs that block and shut down the tiny tubes that form your pet’s kidney apparatus. Without the ability to cleanse its body of waste products, blood levels these wastes that include blood urea nitrogen (BUN) and creatinine rise to toxic levels. Blood phosphorus levels rise as well. That is the point that you would notice something was very wrong. These pets become depressed. They cease eating. They begin to vomit. They may walk with their belly tucked up and show pain in the area of their kidneys. Their urine volume, frequency and color may change (dark or pink = hematuria).

These pets are all showing symptoms of renal (kidney) failure; which indeed, they now have. They have become uremic. You can read more about the symptoms of uremia in dogs and cats here

How Much Antifreeze Does My Pet Have To Drink To Become Sick?

That depends on a number of factors:

Most automobiles run a mixture of 50% antifreeze and 50% water. With time, it is the water that will evaporate and at that point additional pure antifreeze is often poured in (although the correct way is to use a hydrometer/refractometer). It is the total amount of ethylene glycol consumed, not the volume of liquid, that is important in determining how toxic it will be.

Before the pet’s body breaks EG down into toxic products, ethylene glycol is excreted, unchanged in its urine. So, the hydration, water consumption and rate of urination of your pet will affect the severity of symptoms and damage. The more that is eliminated unchanged (peed out), the better.

A dog must consume about one-half to one teaspoon of pure ethylene glycol per pound of body weight to be lethal. (4.4-6.6 ml/Kg). It is about three times more toxic to cats and humans (1.4-1.5 ml/kg) than it is to dogs. However, if the pet receives either therapeutic ethanol or fomepizole treatment in time, it can survive a much larger EG dose.

What If My Pet Gets Ethylene Glycol Products On Its Hair or Skin?

Ethylene glycol is absorbed through the skin. (read here) But a single casual skin contact or brushing up against contaminated surfaces are unlikely to cause health concerns in your pet.  What would be of concern would be a pet licking off a cumulatively toxic dose while grooming. So, any pet that routinely frequents contaminated garages, mechanic shops or junkyards could face this hazard. Unfortunate dogs that are kept in those locations, often for security purposes, do not lead long lives for a number of reasons. Perhaps ethylene glycol exposure is one of them.

How Will My Veterinarian Diagnosis Antifreeze Poisoning?

It is not that likely that your veterinarian will suspect antifreeze exposure in your pet unless you bring that possibility to his/her attention or the pet’s history suggests it.

If you are very fortunate, the veterinarian might notice that your pet exhibits pain when the area around its kidneys is pressed. Your veterinarian might also note characteristic, six-sided or Maltese-cross shaped crystals of calcium oxalate in your pet’s urine – although a few crystals often occur in normal, acidic pH, urine.

If you mention that your pet has begun vomiting, that + the kidney pain might be another clue. If your veterinarian performs an ultrasound examination of your pet’s abdomen, the vet might notice that your pet’s kidneys reflect the ultrasound waves more than they should (increased echogenicity). That particular kidney appearance is not proof of ethylene glycol exposure because many other things can cause it.

If your veterinarian were to pass an ultraviolet lamp (often used as an aid in diagnosing ringworm) over the pet’s urine, the vet might notice that the urine glows (fluoresces). 

But the most important clues of early ethylene glycol poisoning are to be found in your pet’s blood test laboratory results. They are an increased anion gap and osmolar gap, signs that your pet’s blood has become more acidic (metabolic acidosis), due to some compound present in its blood that shouldn’t be there. Lowered blood calcium level (hypocalcemia) do to the pet’s blood calcium having bound to oxalate) is another common finding. Your pet’s blood pH would probably also be lower than normal. 

There are commercial test kits that detect ethylene glycol in the blood of dog and cats. They are most accurate during the first 1-6 hours after EG was ingested and probably not of much value if over 12 hours have passed. The test kit may not be sensitive enough to detect doses of EG that can be toxic to cats and certain medications commonly given to dogs and cats in suspected poisoning cases can cause a false positive test results (certain charcoal antidotes, Valium® and barbiturate solutions and other preparations that might contain propylene glycol). The test kits are not on hand at many local veterinary clinics – check with veterinary emergency centers or human hospital pharmacies in your area before you arrive with your dog or cat.

What Treatment Does My Pet Need If It Drank Antifreeze

Because ethylene glycol is absorbed into the body so quickly, oral medications designed to make a pet vomit up toxic materials (things like hydrogen peroxide solutions) or rinse out its stomach (gastric lavage) are only helpful for the first hour or so. Oral universal antidotes are also ineffective.

What is effective in preventing early damage are compounds that block the body’s conversion of ethylene glycol into its more toxic metabolites. For a long time, that was ethanol (grain alcohol) administered to tie up the pet’s alcohol dehydrogenase enzymes that are required for that toxic process to occur.  Ethanol is still commonly used as the antidote for antifreeze/ethylene glycol poisoning in dogs and cats. It is readily available, inexpensive and very effective in preventing ethylene glycol from forming toxic byproducts. But ethanol does have some drawbacks. It has to be periodically re-administered because it is rapidly metabolized by the liver and lost. Your veterinarian or his/her nurse has to closely monitor your pet to be sure it does not receive toxic amounts. Ethanol in itself can cause coma, respiratory arrest (stop breathing) or liver damage if too much is given.

Those drawbacks in the use of ethanol led to development of an alternative product, fomepizole (4-Methylpyrazole= 4-MP =  Antizol®). Fomepizole does not need to be administered as frequently as grain alcohol, and it does not have the side effects of ethanol. Fomepizole is not recommended for use in cats. Its only disadvantage is its expense. 

Other Things That Must Be Done:

Your pet’s acid-base balance (blood acidity below 7.3) needs to be brought back up to normal. This is done through the administration of fluids that contain sodium bicarbonate and by checking y our pet’s urine and/or blood pH periodically to regulate the amount of antidote given.

Other things can be done to speed the removal of ethylene glycol from your pet’s blood before it has time to break down into toxic products. That is best done by administering intravenous fluids to encourage your dog or cat to urinate the ethylene glycol out of its body. In dogs and cats whose kidneys are still healthy, giving intravenous fluids increase urine flow (GFR) – so fluid administration is important.  If kidney damage has already occurred, the pet will not be able to increase its urine flow. In those cases, a technique called peritoneal dialysis can also help flush out EG. In some large veterinary centers, the same hemodialysis machines used to cleanse the blood of human EG victims have been used on pets as well.

Dogs and cats that are already developing life-threatening complications need other support – things like temperature maintenance and open airways protection (intubation). Some of these dogs and cats develop critically low blood calcium levels that can lead to convulsions. Some veterinarians administer calcium for this problem; but others worry that the added calcium might speed the formation of toxic calcium oxalate, so they give anti-seizure medicines like diazepam or midazolam (Valium®,   Versed®).

Pets will usually recover fully if these things are done within 8 hours of drinking ethylene glycol and continued until blood ethylene glycol levels drop into a safe range. The problem is that most cases are not discovered and treated that rapidly. After more than 18 hours have passed, neither ethanol nor fomepizole will help because the toxic breakdown products of EG have already been released. Most, or all, of the original ethylene glycol has already left your pet’s body by then.

There is no specific treatment that will reverse kidney damage. What one is left with is trying to minimize the damage. At that point, your pet’s fate will rest on the levels of BUN and creatinine in its blood – measurements of how well its kidneys are functioning. Intravenous fluids, peritoneal dialysis, possibly diuretics and stabilization treatments can still help at this time. But recovery will depend on how much the pet’s kidneys have been injured and the extent of their ability to recover. God blessed humans and pets with considerably more kidney tissue than their bodies require – that is why healthy humans can safely donate one kidney. If the pet is fortunate and the amount of EG consumed is not too large, with treatment and time its body will return to equilibrium.

A kidney transplant is an option for some cat owners. It is less successful in dogs. It is an expensive procedure that is only performed at a few large, sophisticated veterinary centers. I would begin by contacting the advanced veterinary center nearest to you that I mentioned in my articles on calcium oxalate kidney stones. You can read about that here for dogs and for cats here. Services provided change. If they do not currently perform kidney transplants they will tell you who does.

What Can I Do To Prevent My Dog Or Cat From Consuming Antifreeze?

Open containers of drained (used) antifreeze and exposure to the spilled liquid, engine leaks or flush are a pet and human hazard throughout the year. In the US, exposure to ethylene glycol is slightly more common from March to May. (read here)  So dispose of drained or partially used containers promptly and safely.

Antifreeze fluid usually has a translucent greenish-yellow color – similar to the above photo. Look for any of this material puddling under your vehicles and have the problem attended to promptly by your mechanic. You can soak up spills with cat litter and wash the garage floor with detergent. Most antifreeze leave a residue that will glow under ultraviolet light.  Alternative car antifreezes that do not contain ethylene glycol (they contain less-toxic propylene glycol or glycerin) are available.

Never pour or store antifreeze in a container that was once used for something else.  There is no valid reason for anyone, other than service mechanics, to keep antifreeze around that is not in use. You can purchase what you need at your local auto store when you need it. If you purchase too much, return the excess. If the container is open, drop it off at your City recycling center.

The bittering agent, denatonium benzoate (Bitrex™), is now often added to antifreeze to make it taste extremely bad. The hope was that doing so would prevent human and pet poisoning. Denatonium benzoate is an atrocious-tasting material. I have accidentally tasted it many times in pet anti-chew sprays, and it tastes simply horrible. Despite that horrid taste, those sprays rarely stop a pet from licking and chewing. The same lack of effectiveness of denatonium benzoate was reported in children. (read here) A law to make it a compulsory addition to all antifreeze sold in the USA failed to pass a number of times. It is opposed by the Consumer’s Union for several reasons. The first is that denatonium benzoate has not been scientifically proven to prevent pets, children or deranged adults from consuming antifreeze. The second is that it is not biodegradable. These organizations also fear that denatonium benzoate will enter runoff water, pass through sewage plants and contaminate surrounding well and groundwater making the water unfit to drink. Some of these organizations also oppose these proposed laws because they grant protection from liability lawsuits to any company that sells bittered ethylene glycol-containing products.

Pets are less likely to consume antifreeze if they are not thirsty. Give your dog and cat plenty of water before taking them out-of-doors on a leash and carry extra water along for long trips. Thirsty dogs will lap at water that could be contaminated with many undesirable things (such as leptospirosis organisms). Dogs that are off-leash are exposed to considerably more hazards of all types than those that are under your control. Of course, your pet’s specific personality and the current location are quite important as well.

If you are suspicious that a puddle or stain may be contaminated with ethylene glycol, check it with a UV lamp (black light) under low lighting. Ethylene glycol has a low vapor pressure which means it does not evaporate or dissipate much over time – so it hangs around.

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