I get a lot of Google search hits about those two drugs, so I thought I'd give the public what it wants. I've mentioned that I still hold some Schering-Plough stock (dog though it's been recently,) and I'm about to do my holdings some minor amount of further harm.
That's because, frankly I don't think very much of Clarinex. I've already written (on March 10) about Sepracor and their role in its development. Fitting in with their business plan, Clarinex is another active-metabolite drug idea.
As I've been mentioning in connection with all the acrylamide business, the liver does a fine job ripping up organic compounds. Most of these altered compounds don't do much except go sluicing out the kidneys, but some of them are active. As it happens, Claritin has one main metabolite, and it still has the antihistamine effect that Claritin itself has. (This situation is becoming less frequent, by the way, since the FDA has come more and more to frown on active metabolites in general. Your regulatory path will be simpler now if you don't have any.)
And it's not an exotic transformation, either. For the organic chemists in the audience, it's loss of an ethyl N-carbamate group, down to the NH. Looking at the structure of Claritin, this is the absolute first thing that any competent medicinal chemist would predict as a main metabolite, and so it is.
That means that if you've taken Claritin, you've taken Clarinex. You starting taking it about twenty minutes after you swallowed the Claritin, when that dose started going through the hepatic portal vein and into your liver. It also means that the synthesis of the compound is essentially identical to Claritin, with really only a one-step difference to change the amine.
And, unfortunately, it also means that Clarinex is one of the more blatant me-too drugs out there, this time an internal one. I can't blame Schering, actually. It was clear for years that they'd need something to take up the slack of the Claritin franchise, and there have been some very good shots taken at that in several therapeutic areas. But none of them have paid off yet, and the company decided to do whatever it took to keep a revenue stream coming in. The other choice was virtuous penury, culminating in firing employees who are now occupied, instead, with finding something more useful. It's hard to see that as a better path.
But that still doesn't make Clarinex any better as a drug. I haven't gone over all the clinical data, but I find it hard to imagine that there's any particular advantage over Claritin. And if perchance there is, I find it hard to imagine that it's worth the price disparity versus (generic) Claritin. I may get some feedback setting me straight on this, but it'll have to be pretty convincing to change my mind.