Amanda Lohin, DVM
MSPCA-Angell West, Waltham GENERAL INFORMATION ABOUT ETHYLENE GLYCOL (EG, ANTIFREEZE)
Ingestion of ethylene glycol (EG/antifreeze) is a true emergency, as it can result in acute kidney failure and death. Please seek emergency treatment if you suspect your pet has ingested antifreeze. Ethylene glycol (EG) is a clear, odorless water soluble liquid used most typically in antifreeze solution. It is also used as an industrial solvent in the manufacture of detergents, paints and lacquers, polishes and other compounds. Most anti-freeze solutions contain upwards of 95% of Ethylene Glycol (EG).
EG is reported to have a pleasantly sweet taste and may have a warming sensation when swallowed. Pets may ingest it for the flavor, out of curiosity, out of necessity (if water bowls are frozen over) or if they are intentionally poisoned.
Dogs and cats are both susceptible to poisoning, but cats are more susceptible. The minimum dose that is lethal in cats is roughly 3 milliliters (mls) per pound body weight. For dogs 9-14 mls per pounds body weight may cause death. Fatality rates for EG intoxication reported by top veterinary schools range from 44–70% for dogs and 78-96% for cats.
EG is absorbed rapidly from the gastrointestinal (GI) tract and distributed rapidly throughout all body tissues. Serum levels can start rising one hour after ingestion and are at their highest 3 hours after ingestion. Usually by 48 hours, serum levels are undetectable due to metabolism and excretion of the drug. Unmetabolized EG is excreted by the kidneys into the urine. The metabolism of EG occurs in the liver.
It was once thought that the unmetabolized form of EG might be toxic to pets. The unmetabolized form of EG can cause central nervous system depression. However it is now thought that byproducts of metabolism of EG cause most of the toxicity. The metabolic by-products including glycoaldehyde, glycolate, glyoxylate, and oxalate all have slightly different properties that may contribute to toxicity.
EG intoxication is classically described in 3 stages. The signs owners may see can vary and are related to the amount the pet ingested.
The first stage occurs 30 minutes to 12 hours after ingestion and is associated with central nervous system (CNS) signs. The following symptoms may be noted: “drunken” or wobbly gait, weakness, seizures, muscle twitching, low body temperature, head tremors, abnormal eye movements, coma, or death. Gastrointestinal symptoms such as vomiting may be seen. Dogs (but not generally cats) will sometimes display excessive thirst. Both species can be seen to urinate more than normal.
Stage two is characterized by changes to the heart and lungs; this stage is less well recognized in pets than in people. Some cats may develop an enlarged heart. Dogs and cats may also develop fluid in the lungs.
Stage three occurs within 24-72 hours of ingestion and is the stage where kidney failure is evident. You may notice that your pet is not eating, vomiting or seems depressed. Bloodwork can show elevations in kidney values.
Rapid diagnosis is crucial. Take your pet to a vet immediately if you think ingestion has occurred. Your veterinarian will start with blood and urine analysis. Certain types of crystals may be seen in the urine and certain blood parameters such as serum osmolality and anion gap will be measured. However, those specific blood and urine changes are not always seen. There are some commercially available test kits that can measure EG in the blood. However, EG may no longer be present at 48-72 hours after ingestion. Because most anti-freeze contains a special dye to help find radiator leaks, your veterinarian can examine vomit and urine with a special light as an additional method for screening; however this is not always reliable.
Treatments for EG intoxication are aimed at preventing absorption, increased excretion and preventing metabolism of the drug. The current drug of choice for inhibiting metabolism EG into its dangerous metabolites is fomepizole (4-methylpyrazole). Hemodialysis is the best option for purifying the blood of EG, but has limited availability. You can assist in the treatment of your pet by seeking PROMPT emergency treatment if you suspect your pet may have ingested antifreeze.
The Humane Society estimates that 10,000 animals die annually from this highly preventable antifreeze poisoning each year.
- Never leave antifreeze containers open, unattended or in reach of pets.
- Make sure any anti-freeze you use contains a “bittering” agent that makes the antifreeze less tasty to pets. Massachusetts passed a law stating that retail and wholesale antifreeze containers sold in the state must contain a bittering agent. Nationally, manufacturers of antifreeze have voluntarily moved to add the bittering agent to antifreeze sold in the consumer market. However, commercial antifreeze may not contain a bittering agent; if you get your car serviced professionally, it may contain the “sweet” EG.
- Do not let your pet roam unattended. Cats should be kept indoors for maximum security. Dogs should be leashed or in a fenced area. Even if you don’t have antifreeze on your property, a pet can easily find leaks on parking lots, in driveways, on farms or near dumps.
- If your pets are outdoors, always make sure they have non-frozen water available to drink so that they do not turn to antifreeze instead.
- Inform your family members about the dangers of EG and contact your veterinarian or an emergency facility immediately if you think there has been ingestion.
For more information about Angell’s Emergency/Critical Care service, please visit www.angell.org/emergency. The Emergency Service at MSPCA-Angell West in Waltham can be reached at 781-902-8400.