GlaxoSmithKline reported positive results from two phase II trials of Promacta -- a non-peptide thrombopoietin receptor agonist (platelet growth factor) which can stimulate the growth and differentiation of bone marrow cells that priduce blood platelets -- for the treatment of chronic hepatitis C-associated thrombocytopenia and chronic Idiopathic thrombocytopenic purpura (ITP). The first study was an international, multicenter, double-blind, randomized, placebo-controlled, dose-ranging study. A total of seventy-four HCV-infected subjects with platelet counts between 20,000 and 70,000/mL were enrolled. The subjects received Promacta (30mg, 50mg, or 75mg daily) or placebo for four weeks (pre-antiviral phase).

The primary endpoint was platelet count increase to greater than or equal to 100,000/mL at week four. The subjects could then initiate antiviral therapy and continue Promacta or placebo for 12 additional weeks (antiviral phase).

The primary endpoint was reached by 75%, 79% and 95% of subjects in the Promacta 30mg, 50mg and 75 mg groups respectively, compared to no platelet elevations in the placebo group (p

A total of 118 subjects with chronic ITP and platelet counts

The primary endpoint was achieved in 28%, 70% and 81% of subjects who received Promacta (30mg, 50mg and 75mg, respectively) compared to 11% of the  placebo group

Phase III trials of Promacta are currently underway.