A consumer watchdog Public Citizen Consumer and Dr. Victor Serebruany, a research professor at Johns Hopkins University, involved in early development of prasugrel, sent a letter to FDA to halt its review of the Lilly's drug prasugrel.

They claim that current dose of prasugeral tested in the trails may be unsafe.

Public Citizen Consumer and Dr. Victor Serebruany, in letter addressed to new FDA Commissioner Margaret Hamburg, said: "We urge the FDA to immediately halt review of this drug until a new Phase 3 study can be conducted with an appropriate lower dose of prasugrel."

It was revealed by the letter that the study of drug involving more than 13,000 patients with acute coronary syndrome showed prasugrel increased the risk of possibly fatal hemorrhage by half compared with clopidogrel, and the risk of fatal hemorrhage fourfold.

Public Citizen's letter said that the dose of prasugrel studied by Lilly was about 2.5 times more potent than the dose of Plavix. The scientists say that the higher dose accounted for the excess bleeding seen with prasugrel. Some patients on prasugrel actually stopped forming blood-clotting platelets completely, putting them at increased risk of hemorrhages.

The letter raised various questions regarding the long term safety of the drug. However despite the cited risk prasugrel was unanimously recommended for approval by FDA's outside advisers.