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

Summary In anecdotal reports, some patients with immune thrombocytopenia ( ITP ) maintained platelet counts after discontinuing romiplostim. Here, we examined rates of platelet response (≥50 × 10 9 /l), remission , splenectomy and adverse events in patients with primary ITP duration ≤6 months who were treated with romiplostim for ≤12 months. The starting dose of romiplostim was 1 μg/kg; concomitant and rescue treatments were permitted to maintain platelet counts. Patients with platelet counts ≥50 × 10 9 /l at the end of 12 months entered a dose taper in which the romiplostim dose was decreased as long as platelet counts were maintained. Remission (platelet count ≥50 × 10 9 /l for 24 consecutive weeks with no ITP treatments) was evaluated in patients once romiplostim was discontinued. Over the 12 months, a high response rate (>90%) was observed. Platelet response occurred quickly (median, ~2 weeks) and was observed for a cumulative median of 11 months. 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 ( NCT 01143038, Amgen 20080435).