Antifreeze Toxicity

By Dr. Beth Guerra

Ethylene glycol, the main ingredient in antifreeze, has long been known to be toxic to household pets. Exposure is usually from puddles under a leaking car or a container in the garage that has been spilled or chewed up by a pet. The minimum lethal dose is only around 2.5 tablespoons for a 20 lb dog or just one teaspoon in a seven-pound cat. The toxic component is not the ethylene glycol itself, but rather the metabolites that form when it is broken down by the liver.

There are three recognized stages to antifreeze poisoning:

Stage 1 (within 30min to 12 hours after ingestion) The pet usually experiences nausea, vomiting, lethargy, or neurological signs and can appear ‘drunk’. Increased thirst and urination may also occur.

Stage 2 (12 to 24 hours after ingestion) An increased respiratory and heart rate may be noted.

Stage 3 (24 to 72 hours after ingestion in dogs, 12 to 24 hours in cats) One of the byproducts of metabolism combines with calcium in the body to form calcium oxalate crystals that damage the kidneys. These crystals can be detected in the urine and can help confirm the diagnosis. A severe metabolic acidosis occurs as well. Oliguric kidney failure develops, characterized by a lack of urine production, can develop at this time. Additional symptoms may include nausea, vomiting, and severe depression.

There are several tests that can be used in dogs to test for ingestion of antifreeze. Some test for ethylene glycol itself, others for the metabolic byproducts. We do have screening tests at ACCES but usually submit the sample to a human hospital for confirmation.

If ingestion was suspected but not witnessed, it is always beneficial to run a test. Treatment varies based on time of ingestion and symptoms at presentation. If ingestion was within 30 minutes and there are no clinical symptoms, decontamination can be attempted with induction of vomiting. In the case of a positive results and symptoms, immediate care should be instituted to avoid impending renal failure. Therapy includes aggressive fluid therapy as well as IV infusions of 4-MP. If 4-MP is not available, intravenous ethanol also works to prevent metabolism of the ethylene glycol to its toxic compounds but causes more side effects. Daily monitoring of blood pH, fluid input, and urination is essential. Symptoms such as vomiting, seizures, or respiratory distress should also be anticipated and treated. Therapy is continued until the test is no longer positive; in some cases this may be several days to weeks. In dogs, the prognosis is favorable if treatment is within 12 to 16 hours and the kidney values are not elevated. In cats, treatment should be within three hours. Once there are signs of kidney failure and crystals, prognosis is grave. The mortality rate in dogs is reported to be 59-70% and is thought to be even higher in cats.

If you have witnessed your pet drink antifreeze, or think exposure has occurred, contact National Animal Poison Control Center; (888) 426-4435 or your veterinarian immediately.