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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

S. Jain1, M. Wojdyla2, C. Bernheisel2, S. Kolodny2, M. Vredenburg2, T. Gernsheimer3

1Rush University Medical Center, Chicago, United States, 2Dova Pharmaceuticals, Durham, United States, 3University of Washington, Seattle, United States

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 2). 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 October 1, 2023.

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