Merck's vorapaxar still in doubt after TRA-2P data presented

The future for Merck & Co's antiplatelet drug vorapaxar remains shrouded even after the presentation of phase III data at the American College of Cardiology meeting over the weekend.

Full results of the 26,449-patient TRA-2P TIMI 50 study were presented at the meeting in Chicago and simultaneously published in the New England Journal of Medicine, and once again sparked debate about the risk: benefit profile of vorapaxar in secondary prevention of cardiovascular events among patients with stable atherosclerosis.

TRA-2P was designed to examine whether adding vorapaxar to standard care in these patients would cut the rate of new myocardial infarctions, strokes, revascularisation procedures and cardiovascular death.

Over three years, adding vorapaxar to standard therapy, including aspirin, reduced secondary cardiovascular events by 12 per cent compared to placebo, but was also associated with a significant increase in moderate and severe bleeding.

Overall, moderate to severe bleeds occurred in 4.2 per cent of patients on Merck's drug compared to 2.5 per cent of the placebo group, and there were twice as many intracranial haemorrhages.

Vorapaxar is a thrombin receptor (PAR-1) antagonist and works in a different way to other anti-platelet drugs on the market.

Presenting the data in Chicago, Dr David Morrow of Brigham and Women's Hospital in Boston emphasised that TRA-2P is the first trial to show that "inhibition of another platelet pathway in addition to standard antiplatelet therapy reduced the risk of recurrent cardiovascular events in long-term secondary prevention".

TRA-2P and another phase III trial in patients with acute coronary syndromes called TRACER were both modified to exclude patients with a history of stroke on the advice of their data and safety monitoring board (DSMB).

Morrow pointed out that vorapaxar's benefits were most apparent among patients with a history of myocardial infarction, adding that "any potential clinical use of vorapaxar would have to be based on appropriate patient selection".

Cardiologists who were not involved with the trial put a less positive perspective on the data. Dr Steve Nissen of the Cleveland Clinic pointed out that 148 fewer cardiovascular events were bought in the study at a cost of 171 moderate and severe bleeds.

Vorapaxar had once been tipped as a potential blockbuster for Merck, and was one of the main pipeline assets at Schering-Plough when Merck bought the company for $41bn in 2009, but has now been largely written off by analysts who feel that it will achieve modest sales even if approved by the FDA.

Merck has not been drawn on its plans for submitting vorapaxar for approval, saying it remains in discussion with cardiologists on how the drug may be used in practice.