Quote Originally Posted by NbyNW View Post
Thanks, Possegal!

Can you explain the difference between H1 and H2 antihistamines to a layperson? I have not heard those terms before.
I can try. I taught that topic YEARS ago in a pharmacology class but let's see what I remember. Histamine can bind to a number of different histamine receptors - H1 and H2 are the prominent ones that the drugs tend to target, but there are H3 and H4 receptors as well. Heck, they may have found some others by now. What the histamine causes to happen, depends on what receptor it binds to. And the receptors are more prominent on different tissues. Such as = you have H2 receptors in your GI and when histamine binds to them, gastric acid secretion increases. So if you block that with an H2 antihistamine like Zantac, less gastric acid, less heartburn. THe H1 receptors are what is involved in allergic reactions. THey exist on a lot of different cells including in your airways, where if stimulated by histamine the bronchioles will constrict. Though I think you also have H2 receptors in the airways that if stimulated dilate the bronchioles. So an H2 blocker is not what you would want if you were having a respiratory reaction allergic response. There are a lot more H1 effects like vasodilation (which would be involved in the edema that you can see with allergies), but I'd have to go look them up.

I'll have to dig a bit more to see how blocking H2 treats hives though. It was quite interesting to see that and now I'm curious. I'm sure much more is known about histamine and its receptors since I had any professional reason to be paying close attention.