Long-term treatment with romiplostim and treatment-free platelet responses in children with chronic immune thrombocytopenia

Abstract

Children with immune thrombocytopenia for ≥6 months completing a romiplostim study received weekly subcutaneous romiplostim (1- 10 μg/kg targeting platelet counts of 50-200×109/L) in this extension to examine romiplostim's long-term safety and efficacy. Sixty-five children received romiplostim for a median of 2.6 years (range: 0.1-7.0 years). Median baseline age was 11 years (range: 3-18 years) and platelet count was 28×109/L (range: 2-458×109/L). No patient discontinued treatment for an adverse event. Median average weekly dose was 4.8 mg/kg (range: 0.1-10 mg/kg); median platelet counts remained >50×109/L, starting at week 2. Nearly all patients (94%) had ≥1 platelet response (≥50×109/L, no rescue medication in the previous 4 weeks), 72% had responded at ≥75% of visits, and 58% had responded at ≥90% of visits. Treatment-free response (platelets ≥50×109/L ≥24 weeks without immune thrombocytopenia treatment) was seen in 15 of 65 patients while withholding romiplostim doses. At onset of treatment-free response, the nine girls and six boys had a median immune thrombocytopenia duration of four years (range: 1-12 years) and had received romiplostim for two years (range: 1-6 years). At last observation, treatment-free responses lasted for a median of one year (range: 0.4- 2.1 years), with 14 of 15 patients still in treatment-free response. Younger age at first dose and platelet count >200×109/L in the first four weeks were associated with treatment-free responses. In this 7-year open-label extension, three-quarters of the patients responded ≥75% of the time, and romiplostim was well tolerated, with no substantial treatment-related adverse events. Importantly, 23% of children maintained treatment-free platelet responses while withholding romiplostim and all other immune thrombocytopenia medications for ≥6 months.