The Food and Drug Administration is reviewing the drug, called prasugrel (also known as Effient), as a therapy for patients with acute heart problems such as heart attacks, who face increased risk of blood clots. Lilly developed the drug with Japanese drug maker Daiichi Sankyo. The FDA has twice delayed a decision on prasugrel.

In a key study, prasugrel was compared against Plavix, co-marketed by Bristol-Myers Squibb and Sanofi-Aventis. The Lilly drug did a better job of reducing the risk of heart attacks, but also seemed to present a higher risk of causing internal bleeding (a classic trade-off with blood thinners).

Data from a 12-month study reviewed by FDA showed that for every 24 serious heart problems the drug prevented, it caused 10 bleeding side effects. Overall, reviewers concluded that prasugrel was associated with three fewer heart-related deaths than Plavix.

Because the companies' clinical trial "demonstrated prasugrel's superiority, not to a placebo, but to an active drug ..., prasugrel's efficacy seems beyond question," FDA staff reviewers said in recommending approval.

Nevertheless every month of delay is costing Lilly and Daiichi Sankyo millions of dollars in lost sales. Moreover some analysts say the drug could ring up more than $1 billion in sales annually by 2012. Rival Plavix took in $4.92 billion in U.S. 2008 sales, according to Bristol-Myers. Sanofi said it will announce sales figures on February 11.

Prasugrel's association with cancer is more difficult to understand, they added, saying the findings could be due to chance. The data showed 27 cases of cancer in prasugrel patients compared to 19 in Plavix. Authorized and specialized advisors will be consulted for the final verdict regarding the risk of malignancy is with Lilly's drug.