Antifreeze and Cats: 6 mL, 2 Hours, One Puddle

Ethylene glycol kills a cat with less liquid than a tablespoon. The lethal dose is about 1.5 mL per kg, so a 4 kg cat is gone at 6 mL, which is 1.2 US teaspoons. It tastes sweet, so the cat drinks it instead of avoiding it, and the treatment window closes at 2 hours, long before most owners see a single sign. A garage is where most exposures happen, and a spill nobody watched leaves no witness except the cat.

Why 6 mL is enough

Ethylene glycol is oxidised by alcohol dehydrogenase to glycolaldehyde, then to glycolic acid, and finally to oxalate. The oxalate binds calcium and crystallises inside the kidney tubules, while the acid load drops blood pH and shuts the kidney down. Absorption is fast: blood levels peak at 1 to 2 hours, and crystals begin forming in the kidney by hour 3. Six millilitres of a 50 percent mix carries 3 mL of pure ethylene glycol, and the dose quoted as the start of kidney damage is 1 to 1.5 mL of concentrate per kg.

Three stages, on a clock

Stage 1 begins 30 to 60 minutes after the cat drinks: it looks drunk, walks wide, vomits, and may seizure between hours 1 and 3. Stage 2 runs from 12 to 24 hours and looks like recovery, which is the trap, because the lungs fill and the heart rhythm changes while the cat eats normally. Stage 3 is kidney failure from 24 to 72 hours, with no urine, then uremic breath and seizures. A cat that seems fine at hour 8 is inside stage 2, not out of danger, and that is exactly when owners stop watching.

The 2 hour window and the antidote

Fomepizole or ethanol blocks alcohol dehydrogenase and has to reach the cat within 2 hours, ideally within 60 minutes. After 3 hours the metabolite load is high enough that the antidote alone will not hold, and the plan becomes 18 to 24 hours of IV fluids plus dialysis where it is available. Activated charcoal binds ethylene glycol poorly, and inducing vomiting helps only inside the first 30 to 60 minutes, and only in a cat that is still alert. Blood work at hour 6 shows the pattern: creatinine climbing, calcium falling, anion gap wide. A clinic without fomepizole will use ethanol, and the dose is calculated to keep a blood level that stops the enzyme without putting the cat to sleep.

Where it hides in winter

Opened jugs sit on garage shelves, drip trays hold 200 to 500 mL, driveway puddles appear after a top-up, and screen wash is 30 to 50 percent ethylene glycol or methanol. A car that overheats in traffic leaves a 20 to 50 mL puddle, and a cat that walks through it grooms its paws clean. One lick takes in 0.1 to 0.2 mL, so 30 licks is the lethal dose for a 4 kg cat. Snow-melt granules and a workshop toilet bowl are the 2 places owners never check.

4 rules for the garage and the driveway

1. Fix every leak the day it appears, and put a drip tray of at least 1 L under any car that marks the floor.
2. Store antifreeze in a sealed 5 L container on a shelf at 1.5 m, never in a bowl, a cup, or a drinks bottle.
3. Blot a spill with 500 g of absorbent, wash the patch with detergent and 10 L of water, then rinse, inside 30 minutes.
4. Walk the garage floor and the driveway every week from November to March, and look under the car after any top-up.

Dose by product, for a 4 kg cat

Product	Active ingredient	Lethal volume	Window
Concentrate	95% ethylene glycol	6 mL	2 hours
50/50 premix	50% ethylene glycol	12 mL	2 hours
Screen wash	30 to 50% glycol or methanol	12 to 20 mL	2 hours
Pet-safe antifreeze	propylene glycol	20 mL and up	4 hours
Snow melt granules	propylene glycol, salts	15 to 30 g	2 to 6 hours

The pet-safe label is not a free pass

Propylene glycol antifreeze is roughly 3 to 5 times less toxic by volume, which is why it carries the pet-safe name, but it is still not water. A cat that drinks 20 mL or more can develop Heinz body anaemia, with pale gums and weakness appearing 24 to 72 hours later, and the salts in snow-melt granules cause vomiting and sodium load at 5 to 10 g per kg. Keep the same storage rules, and read the percentage on the back rather than the picture on the front.

What else looks like antifreeze at 8 p.m.

A drunk walk in winter has several causes and each one is treated differently. An anticoagulant rodenticide gives no sign at all for 3 to 5 days and then starts bleeding; methanol in screen wash behaves much like ethylene glycol and takes the same antidote; a cat that ate rotting fruit can arrive with the same wobble from ethanol. Antifreeze is the fastest killer of the 4, which is why the phone call comes before any diagnosis, and why the container in your hand saves 10 minutes of blood work at 2 in the morning.

At home first, then the phone call

Any suspected lap or drink is a phone call within 5 minutes, because waiting for the drunk walk spends the 2 hour window. Bring the container or a photo of the label. If the paws are wet, wash them with 500 mL of warm water and a drop of dish soap inside 10 minutes, dry, then drive. Do not give milk, oil or salt. If the cat is already wobbly, vomiting or breathing fast, put it in a carrier flat and go now, because at hour 2 the gap between an antidote and dialysis is measured in minutes. Keep the label, or the toxic dose tool, in front of you while you call, since the concentration printed on the back is the first thing the vet needs.

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