CONDITION
Antifreeze (Ethylene Glycol) Toxicity
Ethylene glycol toxicity occurs when a dog or cat ingests antifreeze or certain other household products that contain this chemical. The substance itself causes relatively mild signs at first—often resembling intoxication, with unsteadiness, increased thirst, and sometimes vomiting—but it is rapidly converted in the body to compounds that cause severe metabolic disturbance and, within hours to days, profound damage to the kidneys. The condition can be difficult to recognise in the early window when intervention may still alter the course. Owners most often arrive on this page having witnessed possible access to antifreeze, or observing a sudden change in behaviour, coordination, or thirst in an animal that may have been unsupervised outdoors or near a garage or driveway. Cats tend to be more sensitive than dogs, and the quantity required to cause harm is small. The pattern of signs often shifts over time, sometimes appearing to improve before deteriorating again. This page explores what ethylene glycol toxicity can look like at different stages, what is happening inside the body as the chemical is metabolised, how the condition is investigated through history, examination, and testing, and the approaches that exist for managing it. The shape and outcome of the condition are closely tied to the time between exposure and intervention.
Why this matters now
Ethylene glycol toxicity can occur at any age and in any breed, and is not tied to a particular life stage or genetic predisposition. It tends to be encountered when animals have access to outdoor areas where antifreeze has been spilled or stored, or during colder months when engine coolant may leak onto driveways or be left in containers. Cats may be exposed through grooming paws that have walked through contaminated puddles, and the sweet taste of the substance can make it attractive to both species.
The condition typically unfolds in distinct phases over the course of hours to days. Initial signs—often appearing within 30 minutes to a few hours after ingestion—may include neurological disturbance and gastrointestinal upset, which can then appear to resolve or plateau for a period. This apparent improvement is misleading; during this quieter phase, toxic metabolites are accumulating and beginning to damage the kidneys. By 12 to 24 hours in cats, and 36 to 72 hours in dogs, signs of severe kidney injury tend to emerge, often with a sharp decline in the animal's condition.
Signals & patterns
Early signals
Unsteady gait or wobbly movement
In the first few hours after ingestion, an affected animal may appear drunk or disoriented, with difficulty walking in a straight line, stumbling, or knuckling the paws. This neurological effect is caused by the ethylene glycol itself before it has been metabolised, and can be mistaken for intoxication from other substances or a neurological event.
Increased thirst and urination
Many animals begin drinking noticeably more water and urinating more frequently within the first few hours. This occurs because ethylene glycol initially acts as an osmotic agent in the bloodstream, drawing water into the urine and prompting the body to compensate by increasing fluid intake.
Vomiting or reduced appetite
Nausea and vomiting can appear early, often within the first several hours, as the substance irritates the gastrointestinal tract. Some animals may also show little interest in food, though this sign alone is non-specific and easily attributed to other causes.
Lethargy or quieter behaviour
Affected animals may become unusually quiet, sleepy, or less responsive than normal. This change in mental state can be subtle at first and may overlap with the period of apparent incoordination, making the overall picture resemble general malaise rather than poisoning.
Later signals
Marked reduction in urination
As kidney damage progresses—typically from 12 hours onward in cats and somewhat later in dogs—urine production often drops sharply or stops altogether. This shift reflects severe injury to the filtering units of the kidney and is a sign that metabolic waste is accumulating in the bloodstream.
Rapid or laboured breathing
Animals in the later stages may breathe more quickly or with visible effort, often as a response to metabolic acidosis—a disturbance in blood chemistry caused by the toxic metabolites and failing kidney function. The breathing pattern may appear shallow and fast, or deep and deliberate.
Collapse or profound weakness
Severe cases can progress to an inability to stand, seizures, or unresponsiveness. This represents widespread metabolic failure and is typically seen when kidney injury is advanced and the body can no longer maintain normal internal chemistry.
Click to read about the biological mechanisms
How this is usually investigated
The investigation begins with a detailed history—particularly any witnessed or possible access to antifreeze, garage areas, or outdoor puddles—and an examination of the animal's neurological state, hydration, breathing pattern, and mucous membrane colour. The clinical picture can shift over hours, so findings at presentation may not reflect the full extent of internal change. Laboratory tests are used to confirm exposure, assess the degree of metabolic disturbance, and evaluate kidney function, with the choice and timing of tests shaped by how much time has passed since the suspected ingestion.
Physical examination
Chemistry panel
Urinalysis with sediment
Urine specific gravity
Blood pressure measurement
Options & trade-offs
Management depends on the time elapsed since ingestion, the severity of metabolic disturbance, and the degree of kidney injury already present. The most effective interventions involve blocking the conversion of ethylene glycol to its toxic metabolites, which requires action within a narrow window—typically a few hours. Beyond that window, or when kidney damage is already established, the focus shifts to supportive care and giving the kidneys time to recover, if recovery is possible. Approaches are often combined and adjusted as the animal's condition evolves.
Alcohol dehydrogenase inhibition
This involves giving a substance that competes with ethylene glycol for the liver enzyme alcohol dehydrogenase, slowing the production of toxic metabolites and allowing more of the parent compound to be excreted unchanged in urine. In UK practice this is most often achieved with ethanol, given intravenously or orally under close monitoring, since fomepizole (4-methylpyrazole) is a human-licensed medicine that many practices find difficult to source at short notice. Where fomepizole can be obtained, it can also be used, typically as an intravenous course over around 36 hours.
Trade-offs: Both options tend to be most effective when given early, within around 3 hours of ingestion in cats and 8 hours in dogs; beyond this window, significant metabolite production may already have occurred and kidney damage may be underway. Ethanol is more readily available in general practice but can worsen sedation, acidosis, and dehydration, and requires careful monitoring of fluid and electrolyte balance throughout treatment. Fomepizole avoids these particular effects, though cats require a considerably higher dose than dogs, and access is often limited by cost, supply, and its status as a human medicine.
Haemodialysis or peritoneal dialysis
Dialysis physically removes ethylene glycol and its toxic metabolites from the bloodstream and can partially compensate for lost kidney function by clearing waste products and correcting severe acid-base disturbances. Haemodialysis is more efficient than peritoneal dialysis but requires specialised equipment and is available only at referral centres. Peritoneal dialysis can be performed in a wider range of settings but is slower and less predictable.
Trade-offs: Dialysis is most helpful when initiated early, before irreversible kidney damage has occurred, but it is resource-intensive, expensive, and not universally accessible. Even with dialysis, the outcome depends heavily on the extent of crystal deposition and tubular injury. Animals that survive the acute phase may still be left with chronic kidney impairment.
Intravenous fluid therapy and metabolic support
Fluids are given to maintain hydration, support kidney perfusion, encourage urine production, and help correct metabolic acidosis. Sodium bicarbonate may be added to the fluid regimen when blood pH is dangerously low. This approach is used alongside other treatments in the early phase and becomes the primary focus when alcohol dehydrogenase inhibition is no longer feasible or when kidney injury is already advanced.
Trade-offs: Fluid therapy alone cannot prevent the formation of toxic metabolites or reverse crystal-induced kidney damage, but it can buy time and support the body's own elimination processes. If the kidneys are severely damaged and not producing urine, excessive fluid administration can lead to volume overload, making careful monitoring essential. The response to fluids is often a useful indicator of how much kidney function remains.
Induced emesis or gastric lavage
If the ingestion is witnessed and the animal presents within the first hour or two, emptying the stomach may reduce the amount of ethylene glycol absorbed. Vomiting is induced using an emetic drug, or in some cases the stomach is flushed directly via a tube. This is typically done only if the animal is alert enough to protect its airway.
Trade-offs: Ethylene glycol is absorbed rapidly from the gastrointestinal tract—often within 30 minutes to an hour—so gastric decontamination has a narrow window of usefulness. It is not a substitute for antidote therapy and carries risks if the animal is already showing neurological signs such as sedation or incoordination, as there is a danger of aspiration.
Common misconceptions
"If the animal seems to improve after a few hours, the danger has passed."
Ethylene glycol toxicity often unfolds in phases, with an initial period of neurological and gastrointestinal signs that may appear to resolve or plateau. During this quieter interval, toxic metabolites continue to accumulate and kidney damage progresses silently. The apparent improvement is misleading, and the most severe phase—acute kidney injury—tends to emerge 12 to 24 hours later in cats and 36 to 72 hours later in dogs.
"Antidote treatment will work at any point after ingestion."
The effectiveness of alcohol dehydrogenase inhibitors such as fomepizole is closely tied to timing. Once ethylene glycol has been metabolised to oxalic acid and calcium oxalate crystals have formed in the kidneys, blocking further metabolism offers little benefit. The window for antidote therapy is typically measured in hours—around 3 hours in cats and up to 8 hours in dogs—after which the focus shifts to supportive care and managing the consequences of kidney injury.
"Only large amounts of antifreeze are dangerous."
The toxic dose of ethylene glycol is small relative to body size. In cats, as little as one teaspoon can be lethal, and dogs can be severely affected by a few tablespoons, depending on their weight. The sweet taste of antifreeze can make even small spills or puddles attractive, and grooming contaminated paws can result in significant exposure, particularly in cats.
Related conditions
Acute Kidney Injury
Ethylene glycol toxicity commonly progresses to acute kidney injury as the liver metabolises the antifreeze into toxic compounds that crystallise within kidney tubules and cause profound damage. This kidney injury typically develops 36–72 hours after ingestion in dogs and 12–24 hours in cats, becoming the dominant feature of the condition if early intervention does not occur.
Anticoagulant Rodenticide Toxicity
Both conditions involve household chemical ingestion and share a similar clinical context: an animal with unsupervised outdoor access or exposure to garage and garden products. The initial signs can overlap in their non-specific nature, though the patterns diverge—rodenticide interfering with clotting, ethylene glycol targeting the kidneys—and both carry time-sensitive considerations for intervention.
Allium Toxicity (Onion and Garlic)
Allium toxicity and ethylene glycol poisoning represent different mechanisms of damage—red blood cell destruction versus metabolic disturbance and kidney injury—but both can present initially with vomiting and general malaise, and both may be encountered when investigating possible ingestion in an animal with access to household or food items.
Diabetic Ketoacidosis
Both conditions can produce severe metabolic acidosis—a state in which the blood becomes dangerously acidic—though through entirely different routes. Ethylene glycol generates acidic metabolites directly, while diabetic ketoacidosis arises from ketone accumulation, but the resulting metabolic derangement shares laboratory features and some overlapping signs such as lethargy and altered breathing patterns.
Epilepsy in Dogs
The early neurological signs of ethylene glycol toxicity—unsteadiness, disorientation, and altered mentation—can sometimes be mistaken for a seizure or post-seizure confusion, particularly if the ingestion was not witnessed. The distinction rests on history, the progression of signs, and the metabolic findings that emerge with ethylene glycol poisoning.
If ethylene glycol exposure is suspected or confirmed, the shape of the days and weeks ahead depends on the degree of kidney injury sustained and whether kidney function begins to recover. Some animals regain sufficient function to live comfortably, while others are left with chronic kidney disease that requires ongoing monitoring and adjustment of diet, hydration, and medication. Understanding the broader context of kidney health—what supports it, what strains it, and how it can be monitored over time—can be useful as the picture clarifies.
Last reviewed: 13 September 2026 · Dr Alastair Greenway MRCVS