New treatments in development for chronic idiopathic thrombocytopenic purpura

A new drug application (NDA) has been filed by GlaxoSmithKline (GSK) for eltrombopag (Promacta) and has been granted priority review status. According to the company, eltrombopag would be the first oral thrombopoietin (TPO) receptor agonist, if approved, and is being evaluated as a short-term treatment of previously treated patients with chronic ITP to increase platelet counts and reduce or prevent bleeding. The drug mimics the activity of TPO and promotes growth and production of platelets in the bone marrow.

In a Phase III study of 114 patients with chronic ITP and platelet counts <30,000/microliter, 59% of eltrombopag-treated patients and 16% of those receiving placebo achieved platelet counts >50,000/microliter. In addition, a significantly lower incidence of bleeding was observed in patients receiving eltrombopaq compared with placebo (p=0.029).

Amgen's romiplostim (Nplate) is also a contender in the race for first-to-market. Also a thrombopoiesis-stimulating agent, the biologic is under priority review by the FDA. This agent, administered by subcutaneous injection with doses adjusted weekly based on platelet response, is a Fc-peptide fusion protein that contains two component regions.

According to Amgen, Phase III data met their primary endpoint with 61% of romiplostim-treated patients achieving durable platelet response (weekly platelet count of >/= 50,000 for greater than six of the eight study weeks) compared with 4.8% of patients receiving placebo. The therapy also appeared to diminish the need for rescue medications, such as corticosteroids or IVIG, as no such medications were necessary in study patients who achieved a durable response (p<0.0001). Overall platelet response occurred in 87.8% in patients receiving romiplostim versus 14.3% in the placebo group (p<0.0001).

Amgen was expecting a regulatory decision on romiplostim's Biologics License Application (BLA) by April 23, 2008, but that was recently pushed to July 23, 2008, following submission to the FDA of a risk management program designed for ITP patients. This amendment to the BLA triggered an automatic three-month extension on a final decision, Amgen said. In March, the FDA's Oncologic Drugs Advisory Committee (ODAC) voted unanimously to recommend approval of romiplstim for treating ITP.