Ahead of an advisory panel meeting tomorrow, staffers at the US Food and Drug Administration have said that Amgen’s new blood-clotting drug Nplate appears to be effective but have also highlighted certain safety concerns.

Amgen’s injectable Nplate (romiplostim) will be reviewed by the FDA’s Oncologic Drugs Advisory Committee tomorrow and is hoping to get approval for the product as a treatment for chronic immune thrombocytopaenia purpura. ITP is a rare blood disorder characterised by increased platelet destruction or inadequate platelet production in the blood, which causes an increased risk of bruising and bleeding.

The FDA staffers said that there is currently a significant unmet medical need in treating patients with ITP who have not responded to other treatments, which include low-dose corticoteroids and removal of the spleen and Nplate seems to be safe and effective. However the reviewers added that they had concerns about the product, including an increase in bone marrow fibres known as reticulin, an increase in blood clots and the development of resistance to the treatment.

In addition, the FDA staff also wondered whether the compound may cause or contribute to other blood disorders, such as leukaemia, due to its mechanism of action. The agency noted that 14 of 204 patients had dangerous blood clots after beginning treatment with Nplate, and that risk could increase after patients stop taking the treatment, though the studies filed by Amgen have not yet addressed the issue.

Nevertheless, Amgen, says that the benefit-risk ratio for Nplate "provides a strong basis for regulatory approval" and analysts believe that it could become a $500 million a year product. Michael King of Rodman & Renshaw issued a research note saying that the odds of approval are around 60% in Amgen’s favour.