Eli Lilly and Daiichi Sankyo have filed their much-touted oral antiplatelet prasugrel with US regulators and will be hoping it can challenge Plavix, Sanofi-Aventis and Bristol-Myers Squibb’s blockbuster.

Lilly and its Japanese partner said they have submitted a New Drug Application for prasugrel to the US Food and Drug Administration for the treatment of patients with acute coronary syndrome (ACS) who are managed with percutaneous coronary intervention (PCI), including coronary stenting. The treatment will be marketed as Effient and the companies added that a filing in Europe will follow later this quarter.

The NDA is based on data from several studies, notably the TRITON-TIMI 38 - which evaluated prasugrel against Plavix (clopidogrel) in reducing ischemic events such as non-fatal heart attack, non-fatal stroke and cardiovascular death in over 13,600 patients. As far as Lilly and Daiichi are concerned, the highlights of the study included a 52% reduction in stent thrombosis for patients treated with prasugrel compared with clopidogrel and a 30% relative risk decrease of non-fatal heart attack, non-fatal stroke, or cardiovascular death for diabetics.

Lilly vice president Anthony Ware said the firm was “elated" about the filing and "we feel confident in the strength and completion of this submission package”. He added that “the benefit/risk profile of this compound, in comparison with the current standard of care, has the potential to improve outcomes” for ACS patients undergoing PCI.

However all this elation needs to be tempered by data from the TRITON-TIMI trial which demonstrated that prasugrel-treated patients experienced a statistically significant increase in non-coronary artery bypass grafting major bleeding compared to clopidogrel-treated patients, including higher rates of life-threatening bleeding.

The bleeding problem has split opinion among analysts and even if the FDA looks reasonably kindly on the drug, many observers believe that the agency will insist on additional trials before the green light is given. Plavix is expected to come off-patent in the USA in 2011 and if prasugrel is found to be more effective, it could have peak sales of $4 billion and more if Lilly and Daiichi manage to get the drug onto the market before generic clopidogrel is introduced.