Dustbury rightly complains about Xyzal. How do you pronounce that anyway? Seems to me that most words that start with X, like Chinese Names, not techo-terms like X-Ray, are pronounced like they start with a Z, so why couldn't they name Zyzal? Probably because X is the new Z.
Anyway, this Xyzal sounds a whole lot like Zyrtec (which I take), so why would I want to change? Well, maybe because it works better. Claritin, like Zyrtec, is supposed to help with allergies, but it doesn't work for me.
Now we get into the chemical structure and David W. comments:
A slight error in your post: Zyrtec is actually both enantiomers while Xyzal is just the biologically active one. 10 mg of Zyrtec contains 5 mg of Xyzal and 5 mg of mirror-Xyzal. It’s a patent ploy. Although theoretically the non-active component could have side effects with no corresponding benefit, if that were the case here we’d have seen Xyzal much earlier.What's an enantimomer? Google fills us in:
D/L vs R/S is explained by Wikipedia, it’s a question of whether you’re looking at the whole molecule or just the chirality center: https://en.wikipedia.org/wiki/Dextrorotation_and_levorotation
In chemistry, an enantiomer, also known as an optical isomer, is one of two stereoisomers that are mirror images of each other that are non-superposable, much as one's left and right hands are the same except for being reversed along one axis. Wikipedia