Amgen says that US health regulators have delayed a decision by three months on whether to approve its new blood-clotting drug Nplate.

The company said that the US Food and Drug Administration put back the action date for its priority review of the Biologics License Application for Nplate (romiplostim) for the treatment of thrombocytopenia in adult patients with chronic immune thrombocytopenic purpura. The date has been extended to July 23 from April 23.

The agency’s Oncologic Drugs Advisory Committee voted unanimously to recommend approval of Nplate in March, but following that meeting Amgen provided the FDA with "a robust risk management programme designed to optimize appropriate use of romiplostim in ITP patients". The FDA considers this additional information to be a major amendment to the romiplostim BLA, which triggers a three-month review extension according to current Prescription Drug User Fee Act (PDUFA) rules.

Ahead of the March ODAC meeting, FDA staffers had expressed 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. They also questioned whether the compound may cause or contribute to other blood disorders, such as leukaemia, due to its mechanism of action.

Amgen is still confident that it will get approval for ITP, a rare blood disorder characterised by increased platelet destruction or inadequate platelet production, which causes an increased risk of bruising and bleeding. The firm said that "we look forward to continued productive discussions with the FDA" and the risk management programme adds extra weight to the Nplate file.