Martine A. Rothblatt
Analyst
Yes. Interesting question, Geoff. We really move them both along as 2 forms of our strategic product development. And the way we look at it is that there's a tremendous diversity in the patient population here. Each of those molecules are 2 very different analogs of prostacyclin. They activate different sets of the prostacyclin receptors and they do so in -- with different strains. They also have different side effect profiles, and those side effect profiles are different for different patients. So our goal being to have everyone of the 30,000 U.S. and a comparable number of European PAH patients on one UT therapy or another, it seems wisest for us to bring both of those programs all the way through to approval. So if a particular patient either had a side effect profile or not as much desired improvement with one of the prostacyclin analogs, they could be segued over to the other prostacyclin analog. And you see a similar situation with many drugs. There's, in the PAH space, there's legions of stories of patients who have not improved on Tracleer, and then they're moved over to Letairis and they have a remarkable improvement. I know personally some of those stories. There's also -- I'll admit it, that I do kind of apply some pressure to my sales forces with regard to the PDE-5 because I find it hard to understand why would anybody take a pill 3 times a day in the case of sildenafil, where you could take a pill one time a day, tadalafil. And if you look at the 6-Minute Walk distance result and the side effect profiles, it's very much 6 of 1 and half dozen of the other. And while there is no doubt that the momentum is moving toward tadalafil, as I mentioned at the beginning of my call -- it's now the most prescribed one -- our physicians for whom I have the highest respect, tell me, "Martine, there are some patients who just do better on sildenafil than on tadalafil, even though I have other patients who do better on tadalafil than sildenafil." And this is just part of the pharmacogenomic reality that we all today, in 2013, we're in the dark ages of pharmacogenenomics. We're not yet at the level of the doctor being able to screen our personal genome, much less be able to compare it to the pharmacogenomic profile of different drugs and say, "Aha, this blood-pressure pill or this pulmonary hypertension pill is the best one for you." We're still in the trial and error phase, and some patients will do better on beraprost, some patients will be -- do better on oral treprostinil. We win exactly the same if, or whether they take either of them. So we're going to continue to move both forward and maintain our -- not only 2 shots on goal, but hopefully winning with both shots.