Romiplostim is a peptibody protein that augments thrombopoiesis by activating the thrombopoietin receptor.
In this phase 2, multicenter, open-label study, 28 thrombocytopenic patients with lower risk myelodysplastic syndromes (MDS) were assigned to receive romiplostim 750 μg administered subcutaneously either weekly or biweekly or administered as biweekly intravenous injections for 8 weeks. Patients also could enter a 1-year study extension phase.
At least 1 adverse event was observed in 93% of patients. The most common adverse events were fatigue and headache (18% for both, and 5 events were grade 3 or 4. There was 1 serious treatment-related adverse event in the biweekly intravenous cohort (hypersensitivity). This hypersensitivity resolved without discontinuation of study treatment. No patients developed neutralizing antibodies or bone marrow fibrosis. Of the patients who completed 8 weeks of treatment, 57% had a complete platelet response, an additional 8% had a major platelet response, and 61% did not require a platelet transfusion during this period. Weekly subcutaneous injections achieved the highest mean trough concentrations.
The safety and efficacy profiles of romiplostim in this study suggested that weekly subcutaneous administration of 750 μg romiplostim is an appropriate starting dose for future clinical studies in patients with MDS and thrombocytopenia.