* Trials strongly positive, but some regulatory issues
* Brilinta fails to prove itself in N.American patients
* Pradaxa trial design unusual, heart attack signal a puzzle

BARCELONA - AstraZeneca and Boehringer Ingelheim both unveiled strong results for new heart drugs at the European Society of Cardiology congress at the weekend -- but neither is guaranteed a home run with regulators.

Experts said questions remained about Boehringer's study design and a minor heart attack signal seen with its stroke prevention drug Pradaxa, while AstraZeneca's blood thinner Brilinta had failed to prove itself in North American patients.

Cardiologists meeting in Barcelona still gave both medicines good reviews, and both companies said the data would allow them to file their potential blockbusters with U.S. and European regulators by the year-end.

However, some doctors urged caution.

One of the things in the (Brilinta) trial that jumped off the page was that in the subgroup analysis ... the North American cohort did not show a favourable response, said Clyde Yancy of Baylor University Medical Center in Dallas, who is also president of the American Heart Association.

Is that a statistical fluke? Or is that a circumstance where because of contemporary treatment patterns in the U.S. whatever benefit you might have expected to get from this drug is masked within the morass of everything else we do?

Brilinta's failure to reduce heart risks when compared to Sanofi-Aventis (SASY.PA) and Bristol-Myers Squibb's (BMY.N) Plavix in the North American population could raise questions over U.S. approvability.

Morgan Stanley analyst Andrew Baum said in a note it was one of the key uncertainties that may limit investor enthusiasm for Brilinta in the near term, although he still sees 2015 sales of $2 billion as possible given the strong headline results.

Consensus forecasts ahead of the study were under $1 billion.


Unlisted Boehringer's drug Pradaxa was cheered as a real breakthrough by offering the first potential alternative to 50-year-old warfarin, a notoriously difficult to drug to use. Pradaxa is an important rival to Xarelto from Bayer and Johnson & Johnson, which is around a year behind it in development as a treatment for stroke prevention.
Experts, however, were puzzled by the fact that the rate of heart attack was statistically higher for Pradaxa than warfarin, though still very low in both groups.

There are also uncertainties as to whether the U.S. Food and Drug Administration will approve Pradaxa on the basis of an open-label study, meaning patients and doctors knew which drug was being used, since the agency far prefers double-blind tests.

Boehringer's Chief Executive Andreas Barner believes the trial design should not be a hurdle, given the very strong clinical trial results, but doubts will persist until the FDA gives its verdict.

That, coupled with the mystery heart-attack signal and a side effect of dyspepsia, which caused some patients to discontinue treatment, leaves the door open for follow-up products like Xarelto, according to Alexandra Hauber of JP Morgan.

(editing by John Stonestreet)