AMG 531, a thrombopoiesis-stimulating protein, for chronic ITP.

Background Most current treatments for chronic immune thrombocytopenic purpura (ITP) act by decreasing platelet destruction. In a phase 1–2 study, we administered a thrombopoiesis-stimulating protein, AMG 531, to patients with ITP. Methods In phase 1, 24 patients who had received at least one treatment for ITP were assigned to escalating-dose cohorts of 4 patients each and given two identical doses of AMG 531 (0.2 to 10 μg per kilogram of body weight). In phase 2, 21 patients were randomly assigned to receive six weekly subcutaneous injections of AMG 531 (1, 3, or 6 μg per kilogram) or placebo. The primary objective was to assess the safety of AMG 531; the secondary objective was to evaluate platelet counts during and after treatment. Results No major adverse events that could be attributed directly to AMG 531 occurred during the treatment period; 4 of 41 patients had transient post-treatment worsening of thrombocytopenia. In phase 1, a platelet count that was within the targeted range (50,000 to 450,000 ...