UPDATE 1-Merck says anti-clot drug may be a clear standout

By Ransdell Pierson

NEW YORK, Sept 13 (Reuters) - Merck & Co's experimental drug to prevent blood clots is unlikely to increase bleeding risk, a potential boon to heart patients that would distinguish it from standard treatments, the drugmaker said on Monday.

Industry analysts have dubbed Vorapaxar, now in late-stage trials among thousands of patients with a history of heart disease, Merck's most promising experimental medicine. Cowen and Co predicts it will generate annual sales of $1 billion by 2015.

The once-daily pill would be taken on top of standard anti-platelet clot medicines, such as aspirin and Bristol-Myers Squibb Co's Plavix, to prevent heart attacks and strokes, or to prevent new attacks.

Luciano Rossetti, who heads global scientific strategy for Merck, on Monday told investors at Morgan Stanley's Global Healthcare Conference that the addition of a standard anti-clot drug to aspirin typically increases bleeding risk 40 percent to 45 percent.

'If you do the same thing with a novel mechanism, such as (Vorapaxar), our expectation is you're not increasing the bleeding risk at all,' Rossetti said at the New York meeting.

Bleeding risks can jeopardize regulatory approval of medicines, or dampen commercial demand for products.

Should the lack of bleeding risk for Vorapaxar indeed be borne out by the costly ongoing trials, slated to be completed next year, Rossetti said that safety benefit could set it well apart from current treatments.

'The difference, in terms of mechanism and in terms of bleeding risk is so big that we think there will be two separate categories' of medicines, said Rossetti, a long-time researcher and professor at the Albert Einstein College of Medicine who joined Merck in 2006.

Vorapaxar works through a new mechanism -- by blocking a receptor to thrombin, a protein highly involved in the clotting process. The product, which Merck acquired through its $41 billion merger with Schering-Plough Corp last November, is widely known by its nickname TRA (thrombin receptor antagonist).

(Reporting by Ransdell Pierson; Editing by Maureen Bavdek) Keywords: MERCK/ (Reuters Messaging: [e-mail]; 646-223-6034; [e-mail]) COPYRIGHT Copyright Thomson Reuters 2010. All rights reserved. The copying, republication or redistribution of Reuters News Content, including by framing or similar means, is expressly prohibited without the prior written consent of Thomson Reuters.