Derek Lowe wrote about the first FDA approved deuterated drug, Austedo (deutetrabenazine). This is a really good overview of deuterated drugs and why they are of interest. There were some comments about patentability. And yes, most of this is going to come down to obviousness. Deuteration of therapeutic compounds has been known for a long time. And there are certain persons and companies who have filed applications on adding deuterium to everything under the sun. So it’s hardly a new concept. But is it unobvious?
This Expert Opinion on deuterated drugs and obviousness (from the patent perspective) is fantastic, and chock full of references.
A brief look at deuterated drugs from an IP view (note that there are a lot of applications, which is very different from a granted patent)
Unless you can show something critical about the placement of deuterium (instead of just scattering deuterium anywhere you can), it’s probably obvious. I once used this reference to show that even if you only substitute deuterium for hydrogen at very specific carbon atoms on thalidomide, those particular carbon atoms were known to be troublemakers. There are going to be more pharmacokinetic studies of known therapeutic compounds where people will demonstrate that certain portions of molecules were known metabolic liabilities. So it’s obvious to start there when you add deuterium.