Dog Antifreeze Poisoning
Antifreeze poisoning is common in dogs and cats, and has a high fatality rate if not treated promptly. An increase in antifreeze poisoning is typically seen in the winter months, and again in the spring when antifreeze is drained from cars. The toxic agent in antifreeze is ethylene glycol, and most antifreeze contains approximately 95% ethylene glycol. Antifreeze is readily ingested by most small animals due to it's pleasant sweet taste. Ethylene glycol is highly toxic, and only a small amount needs to be ingested for toxicity or death to occur. The ingestion of as little as a few tablespoons of antifreeze can be fatal to a 30 lb dog. This quantity may easily be ingested from licking antifreeze drippings on a garage floor.
Ethylene glycol is rapidly absorbed from the gut. It is then converted to toxic metabolites in the liver. These toxic metabolites -- glycolaldehyde, glycolic acid and oxalic acid, cause severe kidney damage. Glycolaldehyde is also toxic to the central nervous system.
Ethylene glycol toxicity occurs in two phases. The early phase occurs from 30 minutes to 12 hours after the ingestion of ethylene glycol, before it has been metabolized by the liver to the more toxic metabolites. Early signs of ethylene glycol ingestion are nausea and vomiting, depression, muscle twitching, incoordination, increased thirst and increased urination. Treatment during this early phase is much more effective than treatment later in the course of the disease. Without treatment, signs related to kidney damage predominate 48 to 72 hours postingestion. The increased urination continues as the animal loses the ability to concentrate it's urine. Severe depression, loss of appetite, seizures, and vomiting also commonly occur. By 72 to 96 hours post ethylene glycol ingestion, urine production may stop due to total kidney failure.
Early diagnosis is critical for therapy to be successful. Ethylene glycol toxicity should always be considered if there is history of possibly exposure. Calcium oxalate crystals in the urine are detected consistently in antifreeze poisoning. Crystals may appear microscopically in the urine as early as 3 to 6 hours postingestion, and may persist in the urine up to two weeks. In the early stages before metabolism has taken place, ethylene glycol can be measured by a veterinarian in serum using a commercially available test kit.
Therapy in the early stages is directed towards preventing gut absorption of ethylene glycol, increasing the excretion, and most importantly, preventing it's metabolism to toxic metabolites. The liver enzyme, alcohol dehydrogenase, is responsible for the metabolism of ethylene glycol. If this enzyme is inhibited, decreased metabolism of ethylene glycol occurs, and ethylene glycol is excreted before toxic metabolites are formed. In the dog, the most effective inhibitor is 4-methylpyrazole (4-MP). Ethanol may also be used as a treatment, since liver alcohol dehydrogenase will preferentially metabolize ethanol, leaving glycol intact. The prognosis for successful therapy is excellent if treatment is started within 8 hours of ingestion. Once renal failure has occurred, treatment is not very effective. In the renal failure stage, treatment is supportive to maintain fluid and electrolyte balance, and may be required for weeks to months.
The ingestion of antifreeze should be avoided. An acutely ill dog or cat with any possibility of exposure to antifreeze should be brought to a veterinarian as soon as possible. The earlier treatment is started, the better the chance for survival. New antifreeze products containing propylene glycol rather than ethylene glycol are available. Propylene glycol is considerably less toxic to dogs and cats, and will help decrease the incidence of antifreeze poisoning.