A phase 3 study of the efficacy and safety of avatrombopag in Japanese adults with chronic immune thrombocytopenia.

Avatrombopag is an oral thrombopoietin receptor agonist approved widely for the treatment of adults with chronic immune thrombocytopenia (ITP). However, data in Japanese patients are limited. This confirmatory phase 3, open-label study investigated avatrombopag (initial dose 20 mg/day) in Japanese adults (aged ≥ 18 years) with chronic ITP (≥ 12 months), insufficient response to prior treatment and an average of 2 platelet counts (PCs) < 30 × 10⁹/L. The primary endpoint was the cumulative number of weeks of platelet response (PC ≥ 50 × 10⁹/L) without rescue therapy for bleeding. Secondary endpoints included platelet response rate at Day 8 and safety. In total, 19 patients were enrolled into the 26-week core phase. The mean age was 56.0 years; 78.9% of patients were female. Mean cumulative number of weeks of platelet response was 13.5 (95% CI 9.1-17.8). Platelet response at Day 8 was achieved by 63.2% of patients. In the core phase, adverse events (AEs) occurred in 94.7% of patients and serious AEs in 15.8%. No thromboembolic events or deaths occurred in the core phase. Avatrombopag demonstrated a rapid and durable platelet response and was well tolerated in Japanese patients with chronic ITP. Long-term safety and efficacy are being assessed in the ongoing extension phase.