Ethylene glycol antifreeze is the most common lethal drink in a home garage, and 1.5 ml/kg of the concentrated liquid is enough to kill a cat. For a 4 kg cat that is 6 ml, roughly 1 teaspoon plus a splash. It tastes sweet, so a cat that steps in a drip tray will lick its paws clean and come back for more. Call a veterinarian or a poison hotline first, and never make the cat vomit.
Why 1.5 ml/kg Is the Whole Story
Retail concentrate is 90 to 95 percent ethylene glycol, and the 1.5 ml/kg figure refers to that strength. A 50/50 premix is 45 to 50 percent, so 3 ml/kg of premix delivers the same toxic load as 1.5 ml/kg of concentrate. The liver oxidizes ethylene glycol to glycolaldehyde, then to glycolate, then to oxalate. Oxalate binds calcium and forms crystals that plug the kidney tubules, which is why the damage is permanent long before the cat looks sick.
Do the math by weight, not by eyeball. A 2.5 kg cat crosses the line at 3.8 ml, a 3 kg cat at 4.5 ml, a 4 kg cat at 6 ml, a 5 kg cat at 7.5 ml, and a 6 kg cat at 9 ml. Kitchen measures help: 5 ml is 1 teaspoon, 15 ml is 1 tablespoon, and a bottle cap holds 15 to 20 ml. One overturned cap is therefore 2.5 to 5 times a lethal dose for a 4 kg cat. Anything above 3 ml/kg is close to uniformly fatal without treatment.
The Three Stages, Clocked
Stage 1 covers 0 to 12 hours and looks like a drunk cat. Between 30 minutes and 2 hours you see wobbling, a head pressed into a corner, dilated pupils, drooling, and vomiting. Some cats seem to recover at 6 to 8 hours, which is the cruelest part of this poison: the cat is already in stage 2.
Stage 2 runs 12 to 24 hours and is cardiopulmonary. Breathing climbs to 40 to 60 breaths per minute against a normal 20 to 30, the heart rate sits above 200, pulses feel weak, and body temperature drops below 37.5 C. Stage 3, from 24 to 72 hours, is kidney failure: urine output falls under 1 ml/kg per hour, then stops altogether, the cat refuses food, vomits repeatedly, and may seizure between 36 and 72 hours. Untreated cats usually die at 3 to 5 days.
Timeline: What Happens and What to Do
| Time after lick | What you will see | Action |
|---|---|---|
| 0 to 30 min | Nothing, or mild drooling | Call the vet now, bring the bottle |
| 30 min to 2 h | Wobbling, vomiting, dilated pupils | Drive to the clinic, do not wait |
| 2 to 6 h | Fast breathing, depression, cold ears | Antidote window still open |
| 6 to 12 h | Apparent recovery, then collapse | Blood test, start fluids |
| 12 to 24 h | Labored breathing, weak pulse | Intensive care, dialysis referral |
| 24 to 72 h | Little or no urine, vomiting | Guarded to poor prognosis |
Weight to Volume, in Kitchen Units
| Cat weight | 1.5 ml/kg dose | Teaspoons (5 ml) | Share of a 20 ml cap |
|---|---|---|---|
| 2.5 kg | 3.8 ml | 0.8 | 19 percent |
| 3 kg | 4.5 ml | 0.9 | 23 percent |
| 4 kg | 6 ml | 1.2 | 30 percent |
| 5 kg | 7.5 ml | 1.5 | 38 percent |
| 6 kg | 9 ml | 1.8 | 45 percent |
What the Emergency Vet Does
Fomepizole (4-MP) is the antidote of choice, and ethanol is the older alternative; both are given only on veterinary prescription, and both work by blocking alcohol dehydrogenase so the poison leaves the body intact. The rule of thumb taught in emergency rooms is that fomepizole is worth giving within 3 hours of ingestion, and still worth discussing up to 8 hours if the cat has not yet made urine. Expect intravenous fluids at 2 to 3 times maintenance rate, sodium bicarbonate for acidosis, and a referral for hemodialysis if the cat arrives after 6 hours.
Testing is time dependent, so a negative result early proves little. A blood ethylene glycol test can read positive from 30 minutes to 18 hours after exposure. Calcium oxalate crystals show up in urine at 3 to 6 hours, and blood work at 6 to 12 hours shows rising creatinine, high phosphorus, and low calcium. Mention the exact product, the estimated volume, and the time of exposure; a 5 minute history changes the treatment plan more than any single test.
Look-Alikes That Change the Math
Propylene glycol (PG) antifreeze is marketed as low toxicity, and it is roughly 3 times less potent than ethylene glycol, but a 4 kg cat that laps 30 ml still develops wobbling, vomiting, and a high osmol gap. Windshield washer fluid is usually methanol, which causes the same acidosis and blindness pattern. Premixed 50/50 coolant, brake fluid drips, and solar panel heat-transfer fluid all belong in the same locked cabinet. Read the label for the words ethylene glycol, not for the color: green, pink, orange, and blue products can all contain it at 30 to 95 percent. For a weight-to-volume check on a different product, use the toxic dose tool (/tools/toxic/); for swallowed metal, see the zinc coin guide (/emergency/toxin-zinc-coin-cat/) and the vitamin D guide (/emergency/toxin-vitamin-d-cat/).
First 20 Minutes, Step by Step
- Move the cat away from the spill and shut the garage door, then wash the paws with 200 ml of lukewarm water and mild soap in a sink, not in the yard.
- Do not induce vomiting. Ethylene glycol burns on the way back up as badly as it does going down, and a struggling cat inhales it.
- Bag the container, the cap, and any soaked rag; the label percentage and the missing volume are the two numbers the vet needs.
- Call ahead so the clinic can pull fomepizole from the fridge; many small practices stock 1 or 2 vials and need 20 minutes to locate them.
- Drive, do not watch. A cat that looks fine at 60 minutes is often in stage 2 by 120 minutes, and the survival difference between treatment at 2 hours and 6 hours is the difference between a discharge and a euthanasia.
Prevention That Actually Holds
Store antifreeze in a closed cabinet at floor level or above, never in a coffee cup or a soda bottle. Place a 60 by 90 cm drip tray under every vehicle and empty it into a sealed jug after each oil change. Fix the 2 or 3 slow leaks that stain the driveway, because a 4 kg cat needs only 6 ml. Switch to propylene glycol where the vehicle allows it, and wipe any spill with 2 paper towels plus 10 ml of dish soap, then rinse with 1 liter of water; a sweet puddle that smells like nothing is still a trap for 24 hours.
If you find a cat with antifreeze on its muzzle, treat the clock as already running. Call, bag the evidence, and drive. The number that matters is 1.5, and it is smaller than most people believe.
Frequently asked
How much antifreeze will kill a 4 kg cat?
About 6 ml of concentrated ethylene glycol, which is 1.5 ml/kg. That is roughly 1 teaspoon plus a splash, or 30 percent of a 20 ml bottle cap. A 50/50 premix needs twice the volume, so 12 ml of premix carries the same toxic load as 6 ml of concentrate.
Can I make my cat vomit after it licks antifreeze?
No. Vomiting at home risks aspiration and does not remove enough of the poison to matter, because absorption starts within 30 minutes. Drive to a clinic instead, and bring the container so the vet can read the ethylene glycol percentage and estimate the missing volume.
How long does a cat have before treatment stops working?
The antidote works best within 3 hours and is still worth giving up to 8 hours if the cat is producing urine. After 12 to 24 hours the oxalate crystals have already formed in the kidney tubules, and treatment shifts to fluids and dialysis rather than reversal.