Remission and platelet responses with romiplostim in primary immune thrombocytopenia: final results from a phase 2 study

In anecdotal reports, some patients with immune thrombocytopenia (ITP) maintained platelet counts after discontinuing romiplostim. Here, we examined rates of platelet response (50x10(9)/l), remission, splenectomy and adverse events in patients with primary ITP duration 6months who were treated with romiplostim for 12months. The starting dose of romiplostim was 1g/kg; concomitant and rescue treatments were permitted to maintain platelet counts. Patients with platelet counts 50x10(9)/l at the end of 12months entered a dose taper in which the romiplostim dose was decreased as long as platelet counts were maintained. Remission (platelet count 50x10(9)/l for 24 consecutive weeks with no ITP treatments) was evaluated in patients once romiplostim was discontinued. Over the 12months, a high response rate (>90%) was observed. Platelet response occurred quickly (median, similar to 2weeks) and was observed for a cumulative median of 11months. Remission was observed in 24 patients (32%); there were no significantly predictors of remission. Most (20/24) patients had remission start before the forced taper. No new safety signals were identified. Thus, in patients with early-stage ITP, romiplostim was well tolerated and induced rapid responses, with remission occurring in approximately one-third of patients (NCT01143038, Amgen 20080435).