Antifreeze poisoning in dogs: ethylene glycol toxicity

Overview

Injury can progress as signs change

Ethylene glycol poisoning particularly affects the nervous system, gastrointestinal tract and kidneys. Early intoxication largely results from absorbed ethylene glycol. Acute kidney injury means rapidly developing tissue injury, impaired function or both. Severity ranges from mild injury to kidney failure. Toxic metabolic products are chiefly responsible for kidney damage. Early treatment aims to prevent their formation.

Coolant concentrates may contain up to 95% ethylene glycol. Ready-to-use products are also sold as 50/50 mixtures. Diluted coolant can therefore still cause exposure.

Causes

Sweet fluid and unnoticed exposure

Ethylene glycol tastes sweet, potentially encouraging voluntary drinking. Your dog may also walk through a spill and lick it from the paws. Some brake fluids, transmission fluids and heat transfer fluids can contain it. Identify the ingredients rather than guessing from a general product name.

Toxic metabolites

Ethylene glycol is rapidly absorbed from the gastrointestinal tract, peaking around 1–4 hours. Around 50% is excreted unchanged by the kidneys. The rest is converted into other compounds in the liver and kidneys. Alcohol dehydrogenase starts conversion to glycolaldehyde.

Glycolic acid accumulation causes severe metabolic acidosis, or body acidification. Oxalic acid binds calcium and forms calcium oxalate crystals. Crystals accumulating in renal tubules cause obstruction and tissue injury. Blood calcium can also fall.

Risk factors

Poor storage or disposal of coolant increases exposure opportunities. Puddles may remain beneath parked cars or after draining a cooling system. The estimated minimum lethal amount of undiluted ethylene glycol in dogs is 4.4–6.6 millilitres per kilogram of body weight. Contact your vet even after a small suspected exposure. Young animals may be more susceptible.

Of 15 canine patients in Canada, 6 were young adults under 4 years. A further 5 were puppies under 9 months.

In cold climates, exposures occur particularly from autumn to early spring when coolant is added or changed. Season does not exclude exposure, however. In a Canadian group of 21 pets, 10 cases occurred in summer. The group included 15 dogs and 6 cats, so the summer proportion is not a dog-only risk estimate.

Typical symptoms

Early signs may appear between 30 minutes and 12 hours after ingestion. Around 12 hours, your dog may briefly seem better. Oliguric kidney injury typically develops within 36–72 hours in dogs. You may see:

• Staggering, stumbling and abnormal paw positioning.
• Severe tiredness, confusion or unusual sleepiness.
• Vomiting and appetite loss.
• Increased thirst and urination initially.
• Later reduced or absent urination.
• Faster breathing, weakness or seizures.

The renal phase may also involve diarrhoea, drooling and mouth ulcers. Kidneys may be enlarged and painful. Apparent improvement can therefore belong to the disease course and does not justify longer home observation.

Complications and consequences

Kidney and other organ injury

Brain swelling can develop. The most severe consequence is acute kidney injury that can become irreversible. Low urine production, or oliguria, may progress to anuria, meaning no urine production. Urinary crystals, accumulated blood nitrogen compounds and declining urine output are poor prognostic signs. Other serious findings can include pulmonary oedema and bloody gastroenteritis. Severe acidosis and electrolyte disturbances also impair function.

Delay and outlook

Delayed treatment worsens prognosis. Dogs treated within around 5 hours of ingestion often recover fully. Antidotal treatment can be started within 12 hours of exposure to prevent kidney injury. These are not safe waiting periods: treatment begins as soon as possible.

Of 15 dogs presenting for ethylene glycol poisoning, 5, or 33%, survived to discharge. Every survivor presented within 7 hours of signs beginning. Later renal status after discharge was unknown. At discharge, survivors' urea or assessed kidney blood results were normal.

Diagnosis at the vet

Exposure and routine samples

History investigates possible contact with a coolant puddle, container or vehicle servicing. Without witnessed drinking, diagnosis combines history, examination and laboratory results. Initial tests include a blood count, organ biochemistry, urinalysis and blood gas analysis. Blood gases assess acidosis, which may occur within 3 hours. Raised kidney blood results are called azotaemia and may indicate already advanced injury.

Urine sediment is checked for calcium oxalate crystals. In dogs, crystals may appear within 6 hours of ingestion. Urine concentration may also decline. Ionised calcium can assess possible hypocalcaemia.

Test interpretation depends on timing

Rapid tests detect original ethylene glycol, whose blood concentration falls as it is converted. A late test may therefore be negative despite poisoning. Some methods also produce false positives. Rapid-test samples are taken no earlier than around 1 hour and no later than around 10–14 hours after ingestion. Plasma oxalate can also investigate later exposure. Such samples are tested from around 8–10 hours to 24–36 hours after exposure. Rising serum oxalate is associated with worsening prognosis. Precise concentrations may require a specialist laboratory, delaying results. Treatment can begin on strong suspicion without awaiting confirmation.

Imaging and other supporting findings

Ultrasound may support assessment of kidney injury and poisoning. Dye in some antifreezes may make urine fluoresce under a Wood's lamp. Increased blood osmolality and an altered osmolal gap may support early suspicion. After death, microscopic kidney examination can confirm poisoning.

Treatment

Antidotal treatment prevents toxic metabolite formation

Treatment centres on preventing conversion into kidney-toxic metabolites. Fomepizole is the first-choice canine medicine, inhibiting alcohol dehydrogenase. Ethanol under veterinary supervision is an alternative if the preferred medicine is unavailable. However, its central nervous system depression and glucose-lowering effects need close monitoring. Your vet prescribes treatment; never give alcohol as a home remedy.

Once kidney blood results rise and urine production declines, enzyme inhibition offers little benefit. Original ethylene glycol has then almost entirely been converted. Care shifts towards supporting kidneys and other vital functions.

Inducing vomiting and cleaning the skin

Very early on, your vet may consider inducing vomiting. Rapid absorption nevertheless limits benefits of vomiting or gastric lavage. A dog with neurological signs is not made to vomit because aspiration may occur. Activated charcoal is unlikely to reduce ethylene glycol absorption. Antifreeze on paws and coat is washed away.

Fluids and hospital monitoring

Fluids correct dehydration and support the body. Quantities are reassessed according to balance and continuing losses. In hospital monitoring of acute kidney injury, blood pressure is generally measured 2–4 times daily. Glucose may be checked every 4–6 hours, for example. Urine output is measured to detect declining or absent production.

With acute kidney injury, excessive fluids can accumulate if the kidneys cannot remove them. Overload can cause pulmonary oedema, for example. Large fluid volumes do not repair an injured kidney by forcing urination.

Acidosis and electrolyte disturbances are corrected according to blood tests. A diuretic may increase output without actually improving renal recovery. Severe injury sometimes requires haemodialysis, which cleans blood through an external machine. An anuric patient's outlook without dialysis is extremely poor. During recovery, urine production may increase markedly, requiring fluids adjusted to new losses. This polyuric phase can last several days. Renal failure-related nausea is also treated to support eating and nutrition.

Prevention

Store coolant in closed, clearly labelled containers. Clean spills immediately. Remove old empty containers from reach too, because collected rainwater may contain ethylene glycol. Do not let your dog lick fluid near parked cars or possible leak sites.

A bittering agent does not make antifreeze safe because dogs may still drink it. Propylene glycol alternatives are less kidney-toxic but are not harmless to drink. During autumn boat maintenance, keep your dog away from antifreeze use and nearby puddles. Supervise outdoor activity to prevent exposure. Check whether a substance is poisonous for other household chemical risks.

Important for dog owners

Contact your vet immediately after suspected antifreeze exposure: do not wait for signs. Report possible leaks, vehicle servicing or an open container. Paw or coat contamination matters too because licking can cause ingestion.

Increased urine during recovery does not remove the need for fluid balance monitoring because electrolyte disturbances may develop. After treatment, monitor drinking, output, appetite and vomiting alongside agreed checks. Agree which changes require emergency reassessment and when renal tests will be repeated. Do not interpret reduced staggering as recovery: initial improvement may precede renal signs.

Frequently asked questions

Should I go to the vet without symptoms?

Yes. Do not wait at home for signs after ethylene glycol exposure. Treatment aimed at preventing renal injury is more beneficial early. No signs therefore does not justify delayed contact if your dog drank antifreeze or contacted a leaking product.

Why might my dog initially seem to recover?

Early neurological signs can improve around 12 hours while metabolite injury progresses. Renal signs in dogs often develop within 36–72 hours. Stopped staggering or improved alertness therefore does not establish harmless exposure or justify cancelling investigation.

Can I give alcohol as an antidote?

Ethanol is a veterinary treatment option but requires close monitoring. It can depress the central nervous system and lower glucose. Do not try alcohol at home: take your dog for immediate assessment and selection of appropriate antidotal care and monitoring.

Does a negative test exclude poisoning?

A late test may be negative because it detects original ethylene glycol rather than toxic metabolites. Diagnosis therefore considers exposure, signs and other investigations together. Results cannot be separated from sampling time and overall condition.

Can a dog survive after kidney injury?

Raised kidney blood results and reduced or absent urine markedly worsen prognosis. In severe cases, dialysis can support renal function and remove toxins. An anuric dog's outlook without dialysis is extremely poor, so further options are assessed individually in hospital.

Is propylene glycol antifreeze safe?

Propylene glycol is less kidney-toxic than ethylene glycol but does not make a product harmless to drink. Keep every such chemical in closed, labelled containers out of reach. After ingestion, establish the composition and significance with your vet.