Abstract Number: OC 72.4
Meeting: ISTH 2021 Congress
Theme: Platelet Disorders, von Willebrand Disease and Thrombotic Microangiopathies » Acquired Thrombocytopenias
Background: Avatrombopag (AVA) is an oral TPO-RA. A high proportion of patients (~90%) respond to AVA, but limited information is available regarding the durability of response utilizing clinically relevant loss of response (LOR) definitions.
Aims: Understand the time until patients experienced their first LOR, if any, and their percent of time with a response.
Methods: A Phase 3 study (NCT01438840) enrolled 32 AVA and 17 placebo-treated patients. Subjects who completed the maintenance phase of the Core or discontinued early because of lack of treatment effect were eligible for the Extension Phase, all receiving open-label 20 mg AVA to start again (Figure 1).
Durability of Initial Avatrombopag Response
Patients randomized to AVA who responded and continued into the Extension were included. Response= PC ≥50,000/µL. LOR= PC <30,000/µL for 4 consecutive weeks (LOR-4wk) or PC <30,000/µL on 2 consecutive scheduled visits (LOR-2vis). During Core, visits were weekly or biweekly with 21 over 26 weeks. In Extension, visits were every 3-4 days, weekly, bi-weekly, or monthly with 31 over 96 weeks. Return of response = PC ≥30,000/µL. Patients requiring corticosteroid rescue (n=3) or platelet transfusion (n=1) were considered non-responders for a minimum of 8 weeks and 1 week, respectively.
Results: 29/32 patients responded and 21 continued into Extension Phase. 61.9% (13/21) and 42.9% (9/21) of patients never experienced a LOR-4wk or LOR-2vis respectively. The average time until patients experienced their first LOR, or completed the study, was 8.2 months (LOR-4wk) and 6.9 months (LOR-2vis). Patients maintained their initial response on average for 83.5% (LOR-4wk) and 79.3% (LOR-2vis) of their time in the study (Table 1).
Phase 3 Study Design
Conclusions: Data suggests the initial response to AVA is durable, with up to 62% of patients never experiencing a LOR, and stable, with patients maintaining a response 84% of the time, despite the planned objective of reducing concomitant medications and the required AVA starting dose in the extension.
To cite this abstract in AMA style:
Jain S, Wojdyla M, Bernheisel C, Kolodny S, Vredenburg M, Gernsheimer T. Durability of Platelet Count Response in Patients Treated with Avatrombopag for Immune Thrombocytopenia (ITP): Post-hoc Results from the Phase 3 Core and Open-label Extension Study [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 1). https://abstracts.isth.org/abstract/durability-of-platelet-count-response-in-patients-treated-with-avatrombopag-for-immune-thrombocytopenia-itp-post-hoc-results-from-the-phase-3-core-and-open-label-extension-study/. Accessed September 24, 2021.« Back to ISTH 2021 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/durability-of-platelet-count-response-in-patients-treated-with-avatrombopag-for-immune-thrombocytopenia-itp-post-hoc-results-from-the-phase-3-core-and-open-label-extension-study/