Avatrombopag for the treatment of children and adolescents with immune thrombocytopenia (AVA-PED-301): a multicentre, randomised, double-blind, placebo-controlled, phase 3b study.

Background: Avatrombopag is an oral thrombopoietin receptor agonist (TPO-RA), taken with food without any specific restrictions, approved for the treatment of adults with chronic immune thrombocytopenia (ITP) who have had an insufficient response to a previous treatment. The aim of this study was to assess the efficacy, safety, tolerability, and pharmacokinetic and pharmacodynamic profile of avatrombopag for children and adolescents with persistent and chronic primary ITP.

Methods: AVA-PED-301 is a global, multicentre, randomised, double-blind, placebo-controlled, parallel-group, phase 3b study. Children and adolescents aged ≥1 to <18 years with a confirmed diagnosis of primary ITP for at least 6 months and an insufficient response to a previous treatment were randomly assigned (3:1) to avatrombopag (aged ≥6 years: 20 mg oral tablet once daily; aged ≥1 to <6 years: 10 mg oral suspension once daily) or matching placebo. Doses were titrated to maintain a platelet count of 50-150 × 10⁹ cells per L. The core-phase (12-week double-blind treatment period) full analysis set included all randomly assigned patients; efficacy analysis was performed based on randomised study drug. The safety analysis set included all patients who received at least one dose of study drug in each study phase. The primary endpoint was durable platelet response (proportion of patients with at least six out of eight weekly platelet counts ≥50 × 10⁹ cells per L during the last 8 weeks of the 12-week treatment period in the absence of rescue therapy); the alternative primary endpoint was platelet response (proportion of patients with at least two consecutive platelet assessments ≥50 × 10⁹ cells per L over the 12-week treatment period in the absence of rescue therapy). The trial core phase is complete and was registered with ClinicalTrials.gov (NCT04516967).

Findings: Between March 2, 2021, and Aug 2, 2023, 83 children were screened, with 75 randomly assigned to avatrombopag (n=54; 24 [44%] female; 48 [89%] White) or placebo (n=21; 12 [57%] female; 15 [71%] White). 15 (28%) patients in the avatrombopag group met the primary endpoint of durable platelet response versus no (0%) patients in the placebo group (difference in response rate 28% [95% CI 16-40]; p=0·0077); 44 (81%) patients in the avatrombopag group met the alternative primary endpoint of platelet response versus no (0%) patients in the placebo group (difference in response rate 81% [71-92]; p<0·0001). The most common adverse events across treatment groups were petechiae (n=20), epistaxis (n=16), and headache (n=14). Serious adverse events were reported in five (9%) patients in the avatrombopag group and one (5%) patient in the placebo group. No deaths, thromboembolic events, or grade 3 or higher bleeding events were reported.

Interpretation: Avatrombopag is an effective oral treatment for children and adolescents with ITP for at least 6 months and has a reassuring safety profile in the paediatric population. Avatrombopag could provide an important treatment option for paediatric ITP.

Funding: Sobi.