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January 20, 2011
Merck's Vorapaxar: Bleeding, Indeed
So, as had been suspected, the reason that Merck's thrombin antagonist vorapaxar ran into clinical trouble was excessive bleeding. This is always the first thing to suspect when an anticoagulant has difficulty in human trials.
It's really a delicate balance, the human clotting cascade, and it's all too easy to end up on the wrong side of it. When you think about it, the whole pathway has to be under very tight regulation - I mean, here's the fluid that transports oxygen and nutrients and removes waste. Absolutely crucial to the life of every cell in the body. And here's an option to have that fluid thicken up and turn to jelly, very quickly, and once it happens it can't be reversed. No, you're going to want a lot of safeguards around that switch. But if you lean over too far the other way, well. . .there's a lot of vascular plumbing in the body, and it gets a lot of stress. Leaks and rips are inevitable. You have to have a method for patching holes, and it has to be ready to go everywhere, at all times. Dial it down just a bit too much, and hemorrhages are inevitable. Thus all the different clotting mechanism steps, and the different drugs targeting them.
As Matthew Herper explains at that link above, the prospect for this drug are completely dependent on which side of the line it ends up on. In this patient population, it's already stepped over - another result like this one, and vorapaxar could be completely sunk.
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