Primary thrombocytopenia

Primary objective: To investigate the clinical effectiveness of Rozanolixizumab as a maintenance therapy in participants with primary ITP; Secondary objective: To evaluate the safety and tolerability of Rozanolixizumab

Primary: To determine the platelet response rate at week 6 and to demonstrate that avatrombopag is superior to placebo in Chinese adult patients with chronic ITP. Secondary: To demonstrate the superiority of avatrombopag over placebo based on the platelet response measured at day 8. To demonstrate the superiority of avatrombopag over placebo based on the cumulative number of weeks with platelet response rate measured within 6 weeks (defined as the cumulative number of weeks with platelet count ≥50×109/L in the absence of rescue therapy). To assess the superiority of avatrombopag over placebo in reducing bleeding and rescue therapy. To assess the effectiveness of long-term treatment with avatrombopag. To assess the safety and tolerability of avatrombopag.