Eli Lilly and Daiichi Sankyo have suffered a setback after it emerged that US regulators have, for the second time, delayed their review on prasugrel, the firms’ much-touted oral antiplatelet drug and potential rival to Plavix.

It is the second time that the companies have been informed by the US Food and Drug Administration that it has not completed its review for the prasugrel New Drug Application. Lilly and Daiichi Sankyo are hoping to get approval for the drug, which would be sold as Effient for the treatment of patients with acute coronary syndromes being managed with percutaneous coronary intervention.

Jennifer Stotka, vice president for global regulatory affairs at Lilly, said that “we remain engaged in collaborative and productive discussions with the FDA regarding the details of our application”. She added that “this is a very large, complex submission, and it should not be surprising that delays occur”.

Ms Stotka concluded by saying that the firms “will not speculate on the timing or what the outcome will be. However, the review is very far along, and we remain optimistic”. Her optimism was echoed by John Alexander, Daiichi’s global head of R&D, who said the companies “remain confident in the submission package for prasugrel”.

The FDA announced the first delay in June saying that the weight of supplemental information filed on the drug meant it had to put back its action date by three months to September 26. That day has come and gone and some observers are wondering if the agency is particularly worried about the safety of prasugrel.

A large chunk of the data presented in the NDA comes from the TRITON trial which showed that prasugrel produced a 19% reduction in relative risk for the endpoint of cardiovascular death, non-fatal heart attack or non-fatal stroke when compared with Sanofi-Aventis/Bristol-Myers Squibb’s blockbuster Plavix (clopidogrel). However the data also revealed that prasugrel-treated patients also experienced a statistically significant increase in non-coronary artery bypass grafting major bleeding compared to Plavix.

In an investor note, Tim Anderson of Sanford Bernstein wrote that while “our best guess at this point is that while the review is not yet complete, a final decision by FDA is not likely to require that Lilly and Daiichi Sankyo generate new clinical data”. He goes on to say that the issue “may be a smaller one like finessing the label, the risk management plan” and so on.

Mr Anderson adds that he expects prasugrel to launch in the fourth quarter, but believes that the drug will not turn a profit until 2010. By 2015, the broker has a sales forecast of $950 million, when it will account for 10% of Lilly’s earnings per share.