Ethylene glycol (EG) is a colorless, odorless, sweet-tasting and highly flammable liquid. It is a common ingredient of antifreeze because of its chemical properties that lower the freezing point of water. In fact, most commercially available brands of antifreeze contain up to 95% ethylene glycol. EG is tasty enough to dogs and cats that they will drink it in large quantities, if it is available. Automotive antifreeze is the primary source of ethylene glycol poisoning in domestic dogs and cats. However, EG is also found in paints, solvents, radiator fluid, brake fluid, motor oil, aircraft and runway de-icing products, automobile windshield de-icing fluids, ink, home solar units, solutions used to develop photographs "the old fashioned way" and wood stains, among other products.
Causes of Antifreeze Poisoning
Ethylene glycol (EG) poisoning in dogs (and in cats) is almost always caused by voluntary ingestion of automotive antifreeze products, which usually contain about 95% EG. Cases of malicious poisoning with antifreeze have also been reported. When water sources are limited because they are frozen, antifreeze typically remains in its liquid form due to its lower freezing point. Leaks of antifreeze from automobile engines and radiators are the main source of antifreeze poisoning in pets. The household garage is the most common site of exposure to this toxin.
Once a dog eats or drinks antifreeze or other products that contain ethylene glycol, the toxin is rapidly absorbed into circulation from the gastrointestinal tract. Ethylene glycol can be detected in a dog's blood within less than 30 minutes after it has been ingested. The dog's liver then metabolizes the ethylene glycol into several highly toxic substances within a matter of hours. One of the main metabolites of EG is oxalic acid. Oxalic acid binds to calcium in the animal's blood, causing the formation of calcium oxalate crystals. These crystals travel in the blood through circulation and ultimately lodge in the tissues of the kidneys, causing severe physical and chemical damage. This in turn leads to acute renal failure and, frequently, death. Acute renal failure is the most common cause of death from antifreeze toxicity in domestic dogs.
Prevention of Antifreeze Poisoning
The best (and only) way to prevent a dog from being poisoned by antifreeze is to keep it from coming into contact with that substance. Dogs should be kept away from garages, driveways or other areas where antifreeze may be kept, spilled or leaking. Any puddles of antifreeze should be cleaned up immediately, using kitty litter to sop up the fluid followed by copious wasing with water and detergent. Use of antifreeze products that contain propylene glycol rather than ethylene glycol is highly recommended. Propylene glycol is being called the "safe antifreeze," because it is much less toxic to animals than ethylene glycol. Dogs should also be kept away from all other potential sources of ethylene glycol poisoning, such as paints, solvents, brake fluid, motor oil, de-icing fluids, inks, solutions used to develop photographs and wood stains.
The lethal dose of pure or undiluted ethylene glycol in an average-sized dog is about 1 to 2 teaspoons. In other words, if a dog drinks or licks 2 teaspoons or more of antifreeze that contains ethylene glycol, it probably will die a painful death from kidney failure within a matter of hours. The lethal dose is greater in large and giant breed dogs. It is important for owners to realize that it takes a very small amount of antifreeze to kill their pets.
How Antifreeze Poisoning Affects Dogs
Once ethylene glycol (EG) is metabolized into oxalic acid and binds with calcium in the blood, it forms calcium oxalate crystals that are deposited in the kidneys. At this point, the dog will become very, very ill. Its symptoms will include depression, vomiting, convulsions, gastric irritation (upset stomach) and extreme pain. Seizures, coma and death are common. Obviously, these are highly unpleasant and potentially catastrophic consequences for the dog.
Symptoms of Antifreeze Poisoning
Ingestion of antifreeze can cause a myriad of observable symptoms in dogs. The symptoms of antifreeze toxicity typically develop in three separate stages. Stage 1 usually occurs within approximately 1 hour after the dog ingested the antifreeze and can continue for up to roughly 10 hours. If the dog is kept primarily outdoors, the owner may not even notice the signs of Stage 1 antifreeze intoxication. When the owner does observe signs, they typically resemble signs of alcohol intoxication and include one or more of the following:
Lack of coordination (ataxia)
Stupor ("drunken sailor" behavior)
Excessive thirst/intake of water (polydipsia)
Excessive output of urination (polyuria)
Gastrointestional irritation and discomfort; nausea
Low body temperature (pronounced hypothermia)
Convulsions/seizures (rare in Stage 1)
Coma (rare in Stage 1)
Death (rare in Stage 1)
Stage 2 of antifreeze poisoning in dogs usually occurs between 12 and 24 hours after the dog ingested the antifreeze or other substance that contained ethylene glycol. During this stage, the neurological signs of EG toxicity may wax and wane (come and go), and the dog may seem to return "back to normal." However, unbeknownst to the owner, during Stage 2 the dog may develop:
Rapid breathing (tachypnea)
Rapid heart rate (tachycardia)
Without treatment, the dog will enter Stage 3 of antifreeze toxicity between 24 and 72 hours after it ingested antifreeze or another substance containing ethylene glycol. The consequences of this stage are due almost entirely to the disastrous effects of the toxic metabolites of ethylene glycol on the dog's kidneys. By the time it reaches Stage 3 of antifreeze poisoning, the dog will be in acute and probably irreversible kidney failure. The signs of this terminal stage typically include:
Depression – severe
Lethargy – severe
Weakness - severe
Painful kidneys (severe abdominal pain)
Decreased production of urine (oliguria)
Absence of production of urine (anuria)
Lack of appetite (inappetence; anorexia)
Vomiting – profuse and continuous
Oral ulceration and pain
Excessive salivation (ptyalism)
Low body temperature (hypothermia)
Low blood pressure (hypotension)
Abnormal eye movements (nystagmus)
Dogs at Increased Risk
Any dogs with access to antifreeze or other substances that contain ethylene glycol have an increased chance of being poisoned by ingesting those substances. Antifreeze is thought to have a mildly sweet flavor that is interesting and tasty to domestic dogs. Dogs that live primarily or exclusively outdoors, and those that are permitted to roam freely about the neighborhood, have an increased risk of coming into contact with antifreeze. This is especially true in cold climates. However, it is becoming increasingly common for people to flush their radiator fluid during the summer and fall months as part of routine car maintenance. This has made antifreeze poisoning a year-round problem in companion animals.
How Antifreeze Poisoning is Diagnosed
Antifreeze poisoning is diagnosed based upon the dog's history, presenting symptoms and specific blood testing. Sometimes, the owner will have seen his dog licking antifreeze from spills or puddles under leaking automobile radiators. Less commonly, the dog may have been observed licking antifreeze straight from an open or leaky container. These ingestions are usually witnessed in a driveway or garage, during the fall or winter months, especially in very cold climates. However, most of the time, the dog's owner will not witness his dog eating or drinking antifreeze. Diagnosis then must be made based on swift assessment of the dog's clinical signs and veterinary tests to identify circulating ethylene glycol (EG) levels in the dog's blood.
Blood samples can be accurately assessed in both veterinary and human laboratories for levels of blood ethylene glycol concentrations and, more importantly, for the blood levels of circulating metabolites of EG. While the time turnover for these results is usually quite quick, it may not be fast enough to save the animal in question. Bedside blood tests have been developed to estimate blood EG concentrations, and at least one such test – the Ethylene Glycol Test Kit - is commercially available for use in dogs. Bedside tests assess the levels of EG, not its toxic metabolites. As a result, they must be used within a few hours of the dog's ingestion of antifreeze to be considered reliable. Another common diagnostic test for antifreeze toxicity is called a blood gas analysis. Within 3 or 4 hours post-ingestion of antifreeze, and especially by 12 hours later, the levels of carbon dioxide and bicarbonate in the dog's blood and the pH of its blood will be markedly decreased. Routine blood work, including a serum biochemistry profile, can also be very helpful in diagnosing antifreeze poisoning, as can the results of a urinalysis.
There are a number of more advanced diagnostic tests that can be performed to confirm antifreeze poisoning. Usually, these are not necessary.
The goals of treating a dog with antifreeze poisoning are to try and prevent absorption of ethylene glycol (EG) from the gastrointestinal tract, prevent the conversion of EG to its toxic metabolites, increase the excretion of EG and its metabolites and prevent the development of acute renal failure. Treatment must be implemented very quickly after a dog ingests antifreeze for the outcome to have even a remote chance of being successful.
If a dog is presented for treatment very shortly after it ingests antifreeze, it may be possible to limit gastrointestinal absorption by inducing vomiting (emesis) and/or through a procedure called gastric lavage. These techniques usually are only valuable when they are performed within an hour or so following ingestion of the toxin. Vomiting can be induced by administering activated charcoal, syrup of ipecac or hydrogen peroxide orally. The dog's veterinarian should be consulted about the appropriate amount and procedure for administering these products. Gastric lavage involves passing an orogastric tube through the dog's mouth and esophagus, and ultimately down into its stomach. The contents of the stomach can then be evacuated by the flow of gravity, by siphoning or by suction. After the dog's stomach has been emptied, isotonic fluids can be infused into the stomach to bathe the gastric lining; they will also be removed by gravity, siphoning or suction. This process is usually repeated several times in an attempt to remove as much of the antifreeze or other toxic materials as possible before they are absorbed into the dog's blood stream.
Several antidotes are available to treat antifreeze toxicity, including ethanol and fomepizole. Authorities recommend that only one of these antidotes be used in any given dog; they should not be used together. Fomepizole currently is the antidote of choice, as long as it can be given intravenously within the first 8 hours after the dog has swallowed antifreeze. Fomepizole inhibits the transformation of EG into its most highly toxic metabolite, oxalic acid. Administration of fomepizole can have adverse side effects, although these are generally fewer and less severe than the side effects associated with the administration of ethanol as an antifreeze antidote. Ethanol must be given within the first few hours after antifreeze ingestion for the treatment to have a chance of being effective. Generally, dextrose is added to ethanol to prevent the dog from becoming hypoglycemic (having abnormally low levels of glucose in its blood). Ethanol is also usually administered intravenously in antifreeze poisoning situations. Intravenous fluids usually are necessary as part of the treatment for a dog poisoned by antifreeze.
If appropriate, gastrointestinal protectants can be administered to soothe the stomach and relieve the intestinal irritation that frequently is associated with antifreeze poisoning. Kidney transplantation is slowly becoming a potential option for pets that have developed acute renal failure following ingestion of antifreeze. This surgical procedure is extremely expensive and is only available at a very few veterinary teaching hospitals and specialty referral centers. It has been best described in cats and is not considered to be a realistic treatment option for dogs at this time.
Dogs suffering from antifreeze poisoning are usually very, very sick. If only the renal tubules of their kidneys are affected, the damage may be reversible, although recovery can take weeks to months to years. Dogs that are treated with an ethylene glycol antidote within a few hours of ingesting antifreeze have an excellent prognosis; those treated within 8 hours of ingestion usually will recover, as well. However, as each hour passes, the prognosis worsens, especially if a large amount of antifreeze was ingested.
Ethylene glycol and its metabolites are usually excreted out through the kidneys within 24 to 48 hours. If the dog survives that long, the long-term consequences of antifreeze toxicity may be minimal, and the animal may have a good prognosis. Unfortunately, once a dog develops oliguric kidney failure – in other words, once the dog's kidneys have shut down and are no longer able to produce urine - the prognosis is poor to grave.