Avatrombopag for persistent and chronic immune thrombocytopenia in children: A post hoc analysis of clinical characteristics of response from a phase 3b clinical trial.

Avatrombopag treatment resulted in significantly higher platelet response rates in patients when compared with placebo in a phase 3b study of patients with paediatric immune thrombocytopenia (ITP) (NCT04516967). These post hoc analyses of the 12-week core phase further assessed the efficacy of avatrombopag, considering the influence of baseline characteristics and protocol-defined dose adjustments on the achievement and sustainability of response. The cumulative percentage of patients who achieved a platelet response (2 consecutive platelet counts ≥50 × 109/L) by days 15 and 22 was 70.4% and 75.9%, respectively, with avatrombopag (placebo, 0% at both days). Only minor differences were observed by baseline characteristics. Among the 92.6% of patients (50/54) treated with avatrombopag who achieved a clinically meaningful platelet response (platelet count ≥30 × 109/L), the mean percentage of time with response was 62.5%. Protocol-specified dose holds due to a platelet count >250 × 109/L occurred for 61.1% of patients, which may have impacted the efficacy outcomes. 78.3% of non-durable responders had ≥1 dose holds prompted by a platelet count of 250-400 × 109/L, a platelet count that would not prompt a dose hold in real-world clinical practice. Avatrombopag demonstrated a clinically meaningful platelet response across the clinical and demographic subgroups in this heavily pre-treated and refractory paediatric ITP population.