Alcohol poisoning? Better give you more alcohol.

Why does drinking wood alcohol cause blindness? When would a doctor infuse alcohol for treatment? The answer lies in the fact that there are more types of alcohols than just what we drink.  Alcohol refers to a broad class of chemicals, only one of which is found in beer or wine.

Ethanol is the compound that we are most familiar with. It is a simple molecule consisting of a two carbon chain attached to a hydroxyl group:

The little guy pictured above is the cause of all those great Saturday nights and awful Sunday mornings. Despite how bad ethanol might make us feel the day after imbibing too much of it, our body is pretty good at handling its breakdown (Hangover science).  What the body is not set up for is ethanol's little brother, methanol:

Methanol is the type of alcohol produced by fermenting wood.  The two chemicals might look very similar and both will give you a nice buzz, but methanol ingestion is a medical emergency.  Methanol itself isn't the problem, its what the body does to it that makes it poisonous.  Alcohol dehydrogenase and acetylaldyhyde dehydrogenase, the enzymes that break down simple alcohols, can't tell the difference between the methanol/ethanol and end up poisoning the body.

 

This shows the breakdown of the two molecules. You don't need to know any organic chemistry to see that alcohol dehydrogenase and acetylaldehyde dehydrogenase are doing the exact same thing, just look at the lines.  Alcohol dehydrogenase removes an "H" and adds another bond, or line, to oxygen. Acetylaldehyde dehydrogenase adds an "OH" to the intermediate molecule in both reactions.

In ethanol's case the result is acetic acid, a harmless molecule that can be used for energy.  However, methanol first breaks down into formaldehyde and finally formic acid. Formic acid is nasty. Ants use it to make their stings more potent and in amounts seen with methanol ingestion it destroys the optic nerve causing blindness.

So what can you do for someone that has taken a big swig of wood alcohol? Get them even drunker on the way to the hospital. Alcohol dehydrogenase and acetylaldehyde dehydrogenase both like to work with ethanol much more than methanol.  The trick is to saturate them with ethanol so that they can't break down methanol into formic acid.  The kidneys will slowly filter out methanol before any damage is done.

In fact, an IV infusion of ethanol along with dialysis used to be the preferred treatment in hospitals before the advent of alcohol dehydrogenase inhibitors. These avoid the complications of keeping a patient drunk for 8 hours but they sure take some of the fun out of the treatment.