The debate as to whether Eli Lilly and Daiichi Sankyo’s prasugrel, a potential rival to Plavix, should be approved will go on for some more time yet after US regulators extended the review period on the much-touted oral antiplatelet drug.

The New Drug Application for prasugrel, for patients with acute coronary syndrome being managed with percutaneous coronary intervention, was submitted in December and granted priority review status in February. However, the mountain of supplemental information on the drug, which will be sold as Effient if approved, means the US Food and Drug Administration has put back its action date by three months to September 26.

Lilly's vice president for global regulatory affairs, Jennifer Stotka, said that the firms “remain confident in our prasugrel submission package". She added that the TRITON trial, encompassed a large amount of data from over 13,000 patients.

The delay is not a great surprise given the level of data and talk about the FDA’s lack of resources to complete reviews in time. Interest in the drug which could compete with Plavix (clopidogrel), Sanofi-Aventis and Bristol-Myers Squibb’s blockbuster, centres around 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 Plavix.

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. Prasugrel is perceived as the jewel in Lilly’s pipeline and if it is found to be more effective than Plavix, it could have peak sales of $4 billion and more if the drug gets onto the market before generic clopidogrel is introduced in the USA in 2011.

Meantime Lilly and Daiichi Sankyo also announced that they have started a new 10,00-patient trial, TRILOGY, which is comparing the effects of prasugrel against Plavix in medically managed patients with acute coronary syndromes. John Alexander, Daiichi Sankyo's global head of R&D, said the move “demonstrates our continued commitment to investigate prasugrel”.