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Ethylene glycol or antifreeze poisoning in pets

Time to prepare your ride for winter.
Time to prepare your ride for winter.
(AP Photo/Ng Han Guan)

Ethylene glycol is the primary ingredient of antifreeze but did you know it is also a component of brake and transmission fluids? Most people are aware its sweet taste is the primary attractant for animals but unaware that upon ingestion blood levels can peak in one to three hours and symptoms or visual signs that something is wrong can begin to appear one hour after ingestion. Time is the key with antifreeze poisoning.

Upon ingestion the following occurs:

Approximately 50% is excreted unchanged directly into the urine.

The remaining amount begins a toxic cycle, outlined here briefly.
 ethylene glycol is oxidized by the enzyme alcohol dehydrogenase through several steps to glycolic acid. This is a relatively quick reaction and is responsible for the early appearance of symptoms as metabolic acidosis occurs. This involves the lowering in pH or the increase in acidity of the entire body; a body dependent on a neutral pH for normal function. Symptoms apparent at this point in time include excessive thirst and urination, weakness, vomiting, dehydration and depression.

Glycolic acid is then slowly changed to glyoxylic acid, an extremely toxic form that combines with calcium to form crystals in the urine, kidneys and even the blood vessels of the brain. As conditions worsen and kidney failure develops symptoms expand to include seizures (in addition to worsening of the above symptoms). Untreated pets lapse into a coma and death follows.

Treatment is possible but it is imperative that it begins within hours of antifreeze ingestion. 
 Both available methods of treatment involve either inhibiting or competing with the alcohol dehydrogenase enzyme. Ethanol or grain alcohol is commonly used in suspension and administered intravenously as a competitor of alcohol dehydrogenase; meaning it decreases but does not completely block the cycle. 4 methylprozal or 4MP is an alcohol dehydrogenase inhibitor and therefore blocks the cycle. This is combined with intensive monitoring and correction of body pH. Time is essential because alcohol dehydrogenase is only present in the initial cycle, progression of the cycle past glycolic acid results in severe, irreversible damage to the kidneys.

Safer alternatives do exist.  In recent years a propylene glycol antifreeze formulation with a bitter taste, marketed under the name Sierra, has been developed ( ). Although significantly less toxic than ethylene glycol, the end result not being kidney failure, ingestion can result in symptoms similar to the early stages of ethylene glycol poisoning and the commonly available test for antifreeze poisoning can come up positive for either ethylene or propylene glycol.

If you suspect your pet may have ingested antifreeze contact your veterinarian immediately. Keep pets and children away from vehicles during maintenance and clean up all spills. Don't forget those older cars left on property. Routinely inspect the under-carriage for leakage as everything from antifreeze to oil to metal fragments can pose a hazard to children and pets.