So, you have something that is sweet, tasty and tempting to sip from the bottle (or lick off the garage floor). But it’s also poisonous and can kill when ingested. It isn’t meant to be consumed anyway, so why not make it taste terrible instead? Problem solved! Except it isn’t — at least not when it comes to antifreeze poisoning.
Ethylene glycol (EG), the active ingredient in antifreeze, is odorless, colorless, sweet and deadly. It’s been used for murder and suicide and, dangerously, to enhance the flavor of cough syrup and homebrew. Sometimes people drink antifreeze accidentally, because it looks like a tasty beverage. And dogs lap it up when it’s been spilled, because that’s what dogs do.
To prevent antifreeze poisoning, manufacturers in the US add denatonium benzoate to products containing EG. Also known as Bitrex, it’s the bitterest substance known. It only takes a small taste to get you to make the Mr. Yuk face.
However, studies have found that adding Bitrex does not prevent antifreeze poisoning.
Why doesn’t Bitrex prevent antifreeze poisoning?
The studies don’t say why Bitrex doesn’t prevent antifreeze poisoning. But there are possible explanations.
People drink antifreeze accidentally because it’s bright green, like a sweet drink. And sometimes it’s been poured into an inappropriate container, like a drink bottle. When someone mistakes antifreeze for a drink, it only takes a taste or swallow to realize their mistake. So it isn’t surprising Bitrex wouldn’t change that.
And some people drink antifreeze intentionally because they know it’s poisonous. A bad taste may simply not be enough to discourage someone bent on self-destruction.
Cats and dogs are able to taste denatonium’s bitterness. Cats don’t usually care for sweets anyway, and they really have no use for Bitrex. But there’s no evidence it turns dogs away.
What’s so bad about antifreeze?
Ethylene glycol is good for your car, but it’s hard on your body. It only takes a very small ingestion to put you (or your child, or your pet) in the hospital. The problem isn’t so much the EG itself as its toxic by-products.
First, EG breaks down into glycolic acid. Glycolic acid in small amounts is harmless; in fact, it occurs naturally in many fruits and vegetables. But large amounts circulating in the body can lower pH to dangerous levels.
Then, the glycolic acid breaks down to oxalic acid. In the bloodstream, oxalic acid binds with calcium to form calcium oxalate crystals. This keeps calcium from reaching the muscles, including the heart, that need it to function properly.
The crystals also build up and block blood flow to the kidneys, causing acute renal injury. As the kidneys fail, calcium oxalate crystals may begin to accumulate in other parts of the body such as the heart and joints.
How much antifreeze is poisonous?
For humans, a potentially toxic dose of antifreeze that is 95% EG is about 0.2 ml per kilogram of bodyweight. A lethal dose is estimated to be 1.5 ml per kilogram of body weight. For example:
- Toxic @ 25 lbs = 11 kg x 0.2 ml = 2.2 ml, or less than half a teaspoon. A full swallow for a child is about a teaspoon.
- Lethal @ 25 lbs = 11 kg x 1.5 ml = 16.5 ml, or a little more than a tablespoon; about 3 swallows for a child.
- Toxic @ 150 lbs = 68 kg x 0.2 ml = 13.6 ml, less than a tablespoon. A full swallow for an adult is about a tablespoon.
- Lethal @ 150 lbs = 68 kg x 1.5 ml = 102 ml, or less than half a cup.
What about cats and dogs?
The minimum lethal dose for cats is 1.4 mg/kg, and for dogs 4.4 mg/kg.
- Lethal @ 9 lbs = 4 kg x 1.4 ml = 5.6 ml, a little over a teaspoon.
- Lethal @ 20 lbs = 9 kg x 4.4 ml = 39.6 ml, less than 3 tablespoons.
What to do if you accidentally drink antifreeze
If you take an accidental taste of EG antifreeze and immediately spit it out, rinse your mouth and call poison control (800.222.1222) for advice.
But keep in mind: A full swallow of EG antifreeze requires immediate medical attention.
How is antifreeze poisoning treated?
Antifreeze doesn’t become toxic until enzymes start breaking it down. If the enzymes are prevented from acting on the EG in the first place, antifreeze poisoning can be prevented.
Fortunately, as it happens, those enzymes would much rather partner with ethanol, the kind of alcohol in beer, wine and liquor. So ethanol itself makes a very effective antidote for antifreeze poisoning.
Maintaining a blood alcohol level of 100 to 150 mg/dl ties up enough enzymes to keep EG from being metabolized. The most effective way to give ethanol is by IV, but in an emergency it can be given by mouth.
Of course, there are downsides to keeping a patient drunk, especially if the patient is a pet, a child or an adult who shouldn’t have alcohol. A non-alcoholic antidote called fomepizole binds enzymes without causing intoxication. If fomepizole is available, it will be used instead.
If it’s too late to keep the EG from being metabolized, treatments include sodium bicarbonate for acidosis and dialysis for renal failure.
The less toxic antifreeze
EG antifreeze is still popular and widely available, but it’s also possible to buy antifreeze made from propylene glycol (PG). PG is generally nontoxic and is used in a very large variety of medications, foods and cosmetics. It can be mildly intoxicating in excessive amounts, but so far PG abuse doesn’t seem to be a thing.
PG antifreeze will be labeled “alternative,” “safer,” “low tox” or just “PG.” If it’s in a transparent container it will be pink. It may have a small amount of sodium nitrite added to help prevent corrosion.
Taste changes don’t stop poisonings
The impact of bittering agents on pediatric ingestions of antifreeze
The impact of bittering agents on suicidal ingestions of antifreeze
Overview of ethylene glycol toxicity (veterinary)
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