What's the Difference Between Albuterol and Xopenex?

Although I ended up not going to medical school, I took many pre-med classes in college. I took everything from anatomy and physiology to chemistry and advanced biology classes. One of my least favorite classes was organic chemistry. I’m sure you’ve heard horror stories about that class, even if they are anecdotal. Even though I thoroughly disliked the class, I did learn an awful lot.

Organic chemistry is unique in that it is the study of the molecular foundation of living things. In contrast to inorganic chemistry, which focuses on things that are non-living. In inorganic chemistry, you look at things like metals, noble gases, and inert compounds. In organic chemistry, the focus is on a singular element — carbon. Carbon is the foundation of life. Without it, you wouldn’t be reading this article.

Understanding chirality

One of my favorite concepts in organic chemistry is chirality. According to Merriam Webster, the word chiral means "asymmetric in such a way that the structure and its mirror image are not superimposable. Chiral compounds are typically optically active; large organic molecules often have one or more chiral centers where four different groups are attached to a carbon atom.”¹

An excellent example of something that has chirality is your hands. They look similar. If you put one hand in front of a mirror, you would see the mirror image of it, which would also look like your other hand. But you can’t put one hand on top of the other and have them match up.

If you’ve ever played the game of Tetris, two of the blocks have chirality... the red and the green. If you put either the red or green up to a mirror, you would see the opposite block, but you cannot put the red block on top of the green block, and vice versa, and have them line up. The two shapes are the same, but opposite. They are not superimposable, meaning they cannot be placed on top of each other and line up.

Most people are familiar with a water molecule, H2O. If you put the molecule next to a mirror, the reverse image is exactly the same, and the molecules can be placed on top of each other. The molecule is perfectly symmetrical.

What does chirality have to do with asthma?

Okay, now that we have the science out of the way, what does this have to do with asthma? I'm glad you asked!

Most people are prescribed albuterol as a rescue medicine when they are diagnosed with asthma. It is used to help open up the airways when they get constricted. You’re likely to have an albuterol inhaler laying around the house somewhere.

Albuterol is a chiral compound. It has a left and a right orientation (think left hand/right hand, as described above). In an albuterol inhaler, both left- and right-hand molecules are present. But did you know that only the left-hand molecule is what affects change in the lungs? Yep, that’s right! Wait, no, left! No, right. I mean, correct. Both molecules are present, but only one of them does the dirty work. On the other hand, the right-handed molecule (pun intended) causes those undesirable side effects, like shaking and racing heart.^2,3

I myself am incredibly sensitive to the right-handed molecule. I already have a fast heart rate and the propensity to get the shakes, so when I take albuterol, those symptoms get even worse. But there is a solution... literally, a solution...

Albuterol and Xopenex for asthma treatment

Xopenex is another medication that can be prescribed to help open up the airways, except it’s not another medicine at all. It’s the same thing as albuterol, but instead of having the right and left-hand molecules, it only has the left-handed molecule, which is the one that helps open up the airway. Xopenex, also known as lev-albuterol, has the right-hand molecule removed, therefore causing less of the undesirable side effects.^2,3

So why not just make all rescue inhalers left-handed? Well, expense would be the first reason. It costs more to remove the right-hand molecule. But from what I understand there is still some benefit from the right-hand molecule, just not as much, and given the fact that most people aren’t super sensitive to the side effects, it’s just not cost-effective to produce lev-albuterol.^2,3

I bet you weren't expecting a science lesson from Asthma.net! But I hope you learned something.

Did you take chemistry in high school or college? Let me know in the comments!