Bleeding risk torpedoed Merck's blockbuster vorapaxar study

A week after Merck spooked analysts and investors alike by shuttering one big trial of the late-stage blockbuster contender vorapaxar while dropping a big group of patients from a second Phase III--without offering an explanation--an investigator for one of the trials has revealed that stroke patients in the study demonstrated an increased risk of bleeding after taking the drug. Vorapaxar is designed to reduce the risk of blood clots.

"They have observed an increase in intracranial hemorrhage in patients with a history of stroke that is not outweighed by their considerations of potential benefit," said Dr. Eugene Braunwald, chairman of the vorapaxar trial, in a statement. The nasty surprise Merck delivered last week shaved $8 billion of market value from the company as investors decided to write it off as a lost cause.

But while Braunwald confirmed some expert speculation about what had gone wrong in the trial, the new insights on the stroke risk also added some perspective on the substantial upside that still remains for vorapaxar.

Forbes' Matthew Herper notes that the bleeding risk among stroke patients doesn't kill the program, but it could severely restrict the market potential for the drug. If the drug demonstrates that it can help prevent heart ailments among the 20,000 people still taking it in the trial, without subjecting them to a significantly increased risk of bleeding, then it has a future. And Merck is targeting the $9 billion Plavix market, which would put it alongside Effient, an Eli Lilly therapy that comes with a warning about the risk of bleeding.

Analysts had estimated that vorapaxar could be worth anywhere from $3 billion to $5 billion an added annual revenue for Merck, but those numbers will likely undergo some serious rethinking.

- see the Reuters story
- check out the Forbes piece