Long-Term Treatment with Romiplostim in Patients with Chronic Immune Thrombocytopenic Purpura (ITP): 3-Year Update from An Open-Label Extension Study

Chronic ITP is characterized by increased platelet destruction and suboptimal platelet production. Romiplostim is an investigational Fc-peptide fusion protein (peptibody) being studied for its ability to increase platelet counts in patients with chronic ITP. We report data from an open-label extension study of romiplostim in adult patients with chronic ITP. Collection of safety and efficacy data from long-term treatment of these patients is ongoing. Eligible patients had completed a prior romiplostim study and had platelet counts □50×10⁹/L. Romiplostim was administered subcutaneously once weekly with dose adjustments to maintain a platelet count of 50–250×10⁹/L. As of July 13 2007, 142 patients had been treated with romiplostim. Their median time since diagnosis was 6.4 years (range 0.6–46.4 years). Most were female (67%) and had previously undergone a splenectomy (60%). The median baseline platelet count was 17×10⁹/L (range 1–50×10⁹/L). The median duration of treatment was 65 weeks (range 1–156 weeks). Twenty-nine (20%) patients discontinued the study, 10 (7%) due to adverse events (AEs) [2 each of bone marrow reticulin and thrombosis; 1 each of bleeding, pain, cardiac arrest, pneumonia, hepatic and renal failure, and monoclonal gammopathy of undetermined significance]. Different measures of platelet count response were analyzed; any platelet counts within 8 weeks of receiving rescue medications were excluded from these analyses. Platelet counts were increased from baseline by ≥20×10⁹/L more than 80% of the time in 54% of patients and more than 50% of the time in 73% of patients. Platelet counts remained above 20×10⁹/L more than 90% of the time in 67% of patients and more than 50% of the time in 94% of patients. A platelet count >50×10⁹/L and double baseline was achieved by 30% (42/138) of patients after the first dose, by 51% (71/138) of patients after the third dose, and by 87% (124/142) of patients overall. The durability of platelet count increases was analyzed: platelet counts >50×10⁹/L were sustained for ≥10, ≥25, and ≥52 consecutive weeks in 78% (102/131), 54% (66/122), and 35% (29/84) of patients, respectively. The patient incidence of bleeding events both of any severity and of clinical significance (≥Grade 3) declined over time (Table). AEs were reported in 95% of patients, with most mild to moderate in severity. The most common were headache (37%); nasopharyngitis (32%); and contusion, fatigue and epistaxis (each 30%). AE frequency did not increase with time on study (Table). Bone marrow reticulin was present or increased in 8 patients with no evidence of progression to collagen fibrosis or chronic idiopathic myelofibrosis. Thrombotic events were reported in 7 (5%) patients; 6 had pre-existing risk factors for thrombosis. In conclusion, romiplostim increased platelet counts in most patients for most of the time, and clinically relevant bleeding was reduced over time. Romiplostim was well-tolerated and AEs did not increase with longer duration of treatment.

Table. Summary of patient incidence of AEs by study period