Eisai heart drug looks safe in mid-stage trials

* E5555 appears safe in two Phase II studies

* Drug may lower heart risks but more studies needed

* Researcher says Phase III study would be justified

* Eisai shares up 1.3 percent

STOCKHOLM, Aug 30 (Reuters) - Japanese drugmaker Eisai's 4523.T experimental blood clot preventer E5555 may have the potential to reduce heart attacks, strokes and cardiovascular deaths without increased serious bleeding risks, Japanese researchers said.

Two Phase II clinical trials presented at the European Society of Cardiology congress on Monday showed that while there was a trend towards increased bleeding as the dose of E5555 increased, serious bleeding risks were not significantly higher.

Shinya Goto from Tokai University School of Medicine said the episodes of bleeding experienced by patients were “nuisance” bleeding.

Eisai is one of a clutch of drugmakers racing to develop drugs to compete in a market dominated by Sanofi-Aventis SASY.PA and Bristol-Myers Squibb's BMY.N $9.5 billion-a-year blockbuster Plavix.

Its new drug works in a similar way to Merck & Co's MRK.N more advanced anti-clotting drug vorapaxar which the U.S. company plans to file for regulatory approval next year.

Patients taking E5555 in the two Phase II trials demonstrated a numerically lower incidence of heart problems compared with those on placebo but Goto said the overall number of events was very low and the studies were not powered to show efficacy.

One of the trials involved 241 patients with acute coronary syndrome and the other 263 patients with high-risk coronary artery disease.

Goto said E5555, also known as atopaxar, was worth progressing into final-stage Phase III trials, adding he did not know if Eisai had such a plan for the product.

Shares in Eisai were 1.3 percent higher on Monday. (Reporting by Ben Hirschler; Editing by Dan Lalor)