GlaxoSmithKline has received some good news on the regulatory front after it was announced that US regulators have granted a priority review to the firm’s Promacta, an experimental drug designed to treat a rare blood disorder.

The US Food and Drug Administration will look at Promacta (eltrombopag), an oral platelet growth factor therapy being developed to treat chronic idiopathic thrombocytopenic purpura, or ITP. The speeded-up review means that the agency will decide on whether to approve the drug over a six- rather than 10-month period.

ITP is characterised by increased platelet destruction or inadequate platelet production in the blood, which causes an increased risk of bruising and bleeding. There are estimated to be 60,000 people diagnosed with chronic ITP in the USA and a similar number in Europe and GSK plans to submit a marketing application there in 2008, where it will be sold as Revolade.

Eltrombopag was discovered as the result of a research collaboration, begun in 1997, between GSK and Ligand Pharmaceuticals, whose share price shot up over 8.5% to $3.68 when the FDA’s decision was announced. The priority review “is very encouraging”, said Paolo Paoletti, senior vice president for oncology at GSK, adding that the firm’s goal is to make available “a targeted therapy in oral form for patients to help raise their platelet counts without having to suppress the immune system”.

The fact that Promacta is delivered orally is expected to give the firm an advantage over Amgen’s injectable Nplate (romiplostim) which is set to be reviewed by the FDA’s Oncologic Drugs Advisory Committee on March 12. That treatment also has priority review status.

Analysts believe that Promacta could be a $1 billion product.