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Antifreeze Poisoning

The most commonly used antifreeze compounds contain ethylene glycol, which is toxic to dogs if ingested. The minimal lethal dosage for dogs 4.4 to 6.6 ml/kg of undiluted ethylene glycol, according to Thrall, Grauer and Dial in Kirk's Current Therapy XII. For instance, this means that 3 teaspoonful of antifreeze (15ml) could kill a 27 pound dog. Antifreeze is normally diluted for use in automobiles so more of the diluted solution would have to be ingested to achieve toxic levels. Unfortunately, antifreeze seems to be palatable to dogs and cats and ingestion of large amounts of the solution can occur. Ethylene glycol has similar effects to ethanol (the alcohols recreationally taken by humans). However, it is broken down in the liver into different compounds than ethanol and these metabolic products cause damage to the kidneys and are more toxic to the central nervous system than the ethylene glycol. Antifreeze poisoning normally occurs when pet become exposed to antifreeze leaking from a car's cooling system, when antifreeze is changed, or when it is left out where your dog can find it.

Sometimes antifreeze is placed in home plumbing systems when heat will not be maintained during winter months (such as a summer cottage). When this is done it is extremely important to remember to flush the system well prior to letting pets in the house. Pets have been exposed to antifreeze poisoning maliciously in some instances, as well. There is at least one brand of antifreeze sold in the U.S. that does not use ethylene glycol and is considered to be safer for pets.

After exposure to the ethylene glycol, clinical signs will develop in as short a time as 30 minutes to approximately as long as 12 hours -- depending on the dose ingested. Depression, signs of intoxication similar to alcohol ingestion, vomiting, coma and death may occur among the initial signs of poisoning. These signs normally last less than 12 hours in dogs, causing some owners to think the danger has passed. After the central nervous system (CNS) effects are over, the kidneys are damaged by the antifreeze. In cats this may seem like a continuous thing because the kidney effects often show up just as the CNS signs would have diminished. In dogs the kidney problems usually show up one to three days after ingestion of the antifreeze. Formation of urine drops off until it is not produced at all. This severe renal failure causes vomiting, sores in the mouth, a noticeable increase in oral odor, severe depression and then eventually coma and death.

With antifreeze poisoning it is imperative to remember that treatment must be initiated very promptly for the pet to survive. Dogs do best if treated within five hours of ingestion of the antifreeze -- cats need to be treated even sooner. The chances of survival diminish rapidly 8 hours post ingestion in the dog and 4 hours post ingestion in cats. For this reason, it is extremely important to consider the possibility of antifreeze poisoning almost any time there are unexplained central nervous system disorders that occur acutely in dogs and cats. There are tests specifically for ethylene glycol. An "in-house" test kit is available to veterinarians, and local hospitals are often willing to test for this toxin on an emergency basis when exposure is suspected. Examination of the urine reveals crystals that are highly suspicious of ethylene glycol exposure about six hours after the toxin is ingested, but waiting for these to show up places the pet at risk. Looking for crystals when the timing of exposure is unknown can give good prognostic information, though.

Treatment for this condition is best done with 4-methylpyrazole (4-MP, or fomepizole (Antizol-Vet(TM)), which was recently approved for use in dogs. This medication competes for the liver enzymes that break down ethylene glycol and slow its metabolism down, keeping the serum levels of the toxic metabolites down and allowing them to be excreted safely -- when used early enough. If 4-MP is not available treatment consists of using ethanol, usually intravenously. Ethanol also competes for the same enzymes and inhibits breakdown of the ethylene glycol. The problem is that ethanol itself causes severe central nervous system depression at the dosages necessary and this can have an additive effect with the ethylene glycol. It is still much better to treat when exposure is known to have occurred or is documented by lab work, though.

There are newer brands of antifreeze on the market that use propylene glycol instead of ethylene glycol. Propylene glycol is commonly found in such products as lotions, creams, and toothpaste and is not as toxic as ethylene glycol. If at all possible, it is best to choose an antifreeze that does not contain ethylene glycol.

By following these simple safety tips you can help ensure that you pet has a healthy winter. If you have any questions regarding antifreeze poisoning, you can contact your local veterinarian, or call the ASPCA Animal Poison Control Center at 1-888-426-4435 for 24 hour consultation with a veterinarian trained in toxicology.

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None of this information is guaranteed to be accurate -- always consult your veterinarian prior to making a decision on your pet's health.