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

Summary 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 × 10 9 /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 × 10 9 /L), the mean percentage of time with response was 62.5%. Protocol‐specified dose holds due to a platelet count >250 × 10 9 /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 × 10 9 /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.