GlaxoSmithKline and Ligand face another wait before finding out if regulators in the USA will approve their clotting disorder treatment Promacta.

GSK has announced that the US Food and Drug Administration is still reviewing the New Drug Application for Promacta (eltrombopag) even though the agency had set September 19 as the action date. The firm is trying to get approval for the drug as a treatment for chronic idiopathic thrombocytopenic purpura.

No specific reason was given for the hold-up and Paul Huckle, GSK’s senior vice president for global regulatory affairs limited himself to saying that “our discussions with the agency are progressing well”. At the beginning of June, The FDA’s Oncology Drugs Advisory Committee unanimously voted (16-0) that Promacta should be approved for the short-term treatment of patients with chronic ITP.

The recommendation was based on studies of the drug in the short-term setting, ie six weeks, However FDA staffers had aired their concerns about long-term risks with the drug, an oral, non-peptide thrombopoietin receptor agonist, such as liver toxicity, bleeding following drug discontinuation and potential marrow fibrosis.

If Promacta gets approval, the number of patients able to get access to the drug will be limited due to the short-term restrictions. There are thought to be approximately 60,000 people diagnosed with chronic ITP in the USA and peak sales estimates range from $1 billion to $2.5 billion.

At the end of last month, the FDA approved Amgen’s rival drug Nplate (romiplostim), an injectable compound. That approval is for patients with chronic ITP who do not respond sufficiently to current treatments, such as corticosteroids and immunoglobulin.