Adventures in metabolism: If your cat eats antifreeze, you can ask your vet to get him drunk

The main ingredient in antifreeze is a compound called ethylene glycol (also found in various other products). This stuff is really bad to drink, both for humans and animals.

My friend and colleague Joe Wirth is a cat owner and also a scientist. Recently his cat Bjorn came back smelling like antifreeze.

“It was so strong in his fur,” Joe said. He thinks it must have leaked out of somebody’s car and Bjorn rolled around in it. Because cats lick themselves to get clean, Joe was pretty sure Bjorn had ingested some.

It turned out his veterinarian wasn’t familiar with ethylene glycol poisoning and didn’t have the main drug for it anyway. (He was eventually able to give a blood test confirming dangerously high levels of ethylene glycol though. At those levels kidney failure was a major concern). The option the vet suggested was taking Bjorn to a specialty clinic nearby. But it turned out this was going to cost a significant chunk of Joe’s yearly income.

While he was sitting in the waiting room (it was a busy night in the clinic) Joe read up on things. He found that there’s an older, alternative treatment for ethylene glycol poisoning, which is to give the animal ethanol — the kind of alcohol found in wine and spirits.

So, Joe wound up asking his vet to get Bjorn drunk. “I’ve been reading all about this while I’m sitting here and I know basic biochemistry,” he said. “why isn’t ethanol on the table?”

Eventually the veterinarian concluded they could do it, and after a quick trip to the liquor store (they had no ethanol) he put Bjorn on an IV. This delivered a solution of 20% ethanol every 6 hours over a 24-hour period. (It was important to have the vet do it to make sure the dosing was right — too much ethanol can also be fatal).

To understand why this is a treatment, we should understand what the body does with things we eat. In general, substances we ingest get metabolized. This means the body carries out various chemical reactions on them, converting them into other substances. It does this because it’s trying to obtain useful chemical compounds and extract energy.

It turns out ethanol and ethylene glycol are both handled by the same metabolic machinery. The image below shows the first two steps in the breakdown of each.

The left side of this image represents the reactions for ethanol. The body first converts ethanol into something called acetaldehyde, and then converts that into another substance, acetate. The names aren’t so important for us. What is important though is that if they are not assisted, these reactions happen far too slowly to be useful. Therefore, cats, humans and other organisms make enzymes to help things go faster. Enzymes are the body’s way of accelerating particular chemical reactions. They are catalysts made of protein. (Catalysts are substances that can increase the rate of a reaction without themselves being modified.)

Going back to the breakdown of ethanol, the first step is converting ethanol to acetaldehyde. That’s the arrow on the top left in the diagram above. This reaction involves an enzyme called alcohol dehydrogenase (ADH). The next reaction (arrow on the lower left) involves an enzyme called aldehyde dehydrogenase (ALDH) converting acetaldehyde to acetate. From here acetate can be broken down and converted further. I’m not showing subsequent reactions, but they all have their own enzymes as well.

Breaking down ethanol is a normal process for a cat or a human. Ethanol is bad for you (especially in large amounts), so it’s a good thing to convert it to other substances.

It turns out however that the enzymes which act on ethanol also act on ethylene glycol. This is because the chemical structures are similar enough between the two compounds. When a cat ingests antifreeze, alcohol dehydrogenase (ADH) converts ethylene glycol into glycoaldehyde. And the next enzyme in the pathway, aldehyde dehydrogenase (ALDH), converts glycoaldehyde into glycolate.

And that’s where the problem arises. Glycolate is toxic (as are some things that it later gets converted into). Having that stuff hanging around eventually leads to kidney damage.

So why does treating a cat with ethanol help avoid ethylene glycol poisoning? It has to do with the enzymes. Basically, you’re trying to keep those enzymes busy with ethanol, so that they don’t have time to act on the ethylene glycol. If that happens, then the body will remove the ethylene glycol without breaking it down, and the cat will be ok.

Or mostly ok.

Before Bjorn could go home, he got washed twice with dish soap. (There was still ethylene glycol on his coat.) And when he did get home, he was still drunk. Joe said, it was “sort of like watching a trailer out of control behind a truck, his back legs just weren’t in sync with his front.”

The treatment had prevented a lot of ethylene glycol from being converted into toxic breakdown products, but almost certainly some of those products did get produced. Joe was wondering whether enough had been produced to damage Bjorn’s kidneys.

He watched Bjorn carefully. The next day he “wasn’t really that hungry. He drank a lot of water and just lay around all day.”

These are some of the symptoms of kidney failure in a cat, but they’re also the symptoms of a hangover. Joe waited one more day, and the next morning Bjorn was back to normal.

Evidently, he’d had a monster hangover, but got over it. He’s been in good health since then.

Finally, let me emphasize that it was important that Joe took Bjorn to a veterinarian. The vet could confirm Bjorn had ingested ethylene glycol, and give treatment in a controlled way. If you are a cat (or dog) owner, and think your pet has ingested ethylene glycol, trying to give it ethanol yourself is a terrible idea. You could give it ethanol poisoning or even kill it that way.

Here’s a picture of Bjorn (and Joe), now feeling better: