GlaxoSmithKline has submitted a New Drug Application to US regulators in a bid to get approval for Promacta, its experimental drug designed to treat a rare blood disorder.

The firm is asking the US Food and Drug Administration to give the green light to Promacta (eltrombopag), an oral platelet growth factor therapy being developed to treat chronic idiopathic thrombocytopenic purpura, or ITP. This is a rare disorder characterised by increased platelet destruction or inadequate platelet production in the blood, which causes an increased risk of bruising and bleeding.

People with chronic ITP often bleed from small blood vessels causing bruises, nosebleeds or even fatal gastrointestinal or intra-cerebral bleeds. Health officials estimate that between 50,000 and 100,000 individuals have the disorder in the USA.

The NDA submission is supported by “the largest database of clinical trial information on investigational therapies for chronic ITP patients”, GSK noted. In a Phase III study, patients on the trial were randomised to either placebo (38 patients) or eltrombopag 50mg (76 patients) once daily for six weeks though the latter dose could be increased to 75mg in patients not responding after an initial three weeks of treatment. At the end of the trial, 59% of eltrombopag-treated patients and 16% on placebo treated patients achieved a platelet count of more than 50,000/microlitre.

Paolo Paoletti, senior vice president of the Oncology Medicine Development Centre at GSK, said that patients with chronic ITP do not have a treatment option that offers the convenience of an oral platelet growth factor. He added that the firm is hopeful that, if approved, Promacta will provide “a new, convenient and effective option for treating this difficult disease”.

GSK plans to seek approval to sell Promacta under the tradename Revolade in Europe in 2008 and the European Medicines Agency's Committee for Orphan Medicinal Products adopted a positive opinion on the drug in June. Analysts believe it has the potential to be a $3 billion blockbuster.