Treatment with the thrombopoietin receptor agonist (TPO-RA) avatrombopag led to durable platelet count responses in patients with immune thrombocytopenia (ITP), with responses among both patients who had received fewer than three prior treatments and those who had received three or more, according to results from a post hoc analysis of a phase III trial.
Michael Vredenburg, PhD, from Dova Pharmaceuticals, presented these findings at the 2020 ASH annual meeting.
Earlier clinical trials have shown that treatment with avatrombopag leads to rapid increases in platelet counts in patients with ITP that are maintained in the target range of 50 to 150×109/L with chronic dosing. In this analysis, researchers sought to understand how the number of prior ITP treatments affected the efficacy of avatrombopag.
This post hoc analysis used data from a six-month, multicenter, randomized, double-blind, phase III study published in 2018, which enrolled 32 patients who were treated with avatrombopag and 17 patients who received placebo. Participants were segmented based on the number of previous ITP treatments (<3 or ≥3).
Patients randomized to study drug received a starting dose of avatrombopag 20 mg daily, which was then adjusted to a dose ranging between 5 or 40 mg daily during the dose titration and maintenance phases, based on protocol-specified parameters.
In comparing avatrombopag-treated patients based on number of prior ITP medications, those who received three or more prior ITP medications appeared to have more refractory disease. For example, 42% had been splenectomized (vs. 0 in the group with <3 prior ITP treatments), and 53% had received prior TPO-RAs (vs. 15%). Also, about two-thirds of patients in the group with three or more prior ITP medications had a baseline platelet count of ≤15×109/L (vs. 39%).
In the entire study population, the median cumulative number of weeks of platelet count response (≥50×109/L) was 12.4 in the avatrombopag group, compared with zero in the placebo group (p<0.0001).
For the 13 patients receiving fewer than three prior ITP treatments, responses lasted for a median of 13.7 weeks; for the 19 patients receiving three or more prior ITP treatments, the median duration of platelet count response was 11 weeks. Dr. Vredenburg added that the proportions of avatrombopag-treated patients achieving a platelet count response at least once during the study were similar, regardless of the number of prior ITP treatments (TABLE).
Platelet count responses also appeared to occur early, with approximately two-thirds of avatrombopag-treated patients achieving a response by day 8, and were durable, with nearly one-third achieving a response in 6 of the final 8 weeks of the study.
Based on these data, the authors concluded that the number of prior ITP treatments did not definitively predict platelet count response to avatrombopag, though “on some measures the group receiving less than three prior ITP treatments fared slightly better,” Dr. Vredenburg noted. Together, “these data suggest that avatrombopag efficacy is relatively consistent, even if a patient has received multiple prior ITP therapies before avatrombopag initiation.”
These findings are limited by the nature of the post hoc analysis, which is potentially biased.
Blinder M, Vredenburg M, Tian W, et al. Consistent efficacy demonstrated by avatrombopag in immune thrombocytopenia (ITP) regardless of the number of lines of prior ITP treatment. Abstract #835. Presented at the 2020 American Society of Hematology Annual Meeting, December 5, 2020.