The US Food and Drug Administration has granted breakthrough therapy designation for GlaxoSmithKline's thrombocytopenia drug Promacta for a rare bone marrow disorder.

Specifically the agency will give support to Promacta/Revolade (eltrombopag) for the treatment of cytopenias in patients with severe aplastic anaemia (SAA) who have had insufficient response to immunosuppressive therapy. SAA is a rare disorder in which the bone marrow fails to make enough new blood cells and there are no approved therapies.

Of those patients unresponsive to initial IST, approximately 40% die from infection or bleeding within five years of their diagnosis. The breakthrough designation was based on the results from a Phase II National Institute of Health study of Promacta in 43 heavily pre-treated SAA patients.

Breakthrough designation differs from the FDA's other fast-track programmes, such as accelerated approval and priority review, as it involves more intensive guidance from the agency on putting together an efficient drug development programme.

Promacta is partnered with Ligand Pharmaceuticals and the latter's chief executive, John Higgins, said the drug "continues to be the basis of ground-breaking and promising science in important areas with significant unmet medical needs".