Phase 1/2 Trial Shows Promise for Rilzabrutinib in Patients with ITP


Principia Biopharma announced positive data on the durability of response from an ongoing phase 1/2 trial of the investigational treatment in patients with immune thrombocytopenia.

Positive data on the durability of response from an ongoing phase 1/2 trial of the investigational treatment, rilzabrutinib, in patients with immune thrombocytopenia (ITP) was announced by Principia Biopharma, the developer of the agent.1

“We are very pleased with the consistency of responses and durability of effect observed among the patient responders. This data provides confidence to move forward to a pivotal phase 3 trial, and assuming no future COVID-19 related impact, our goal is to initiate the trial by the end of 2020,” Dolca Thomas, MD, chief medical officer at Principia, said in a press release.

In this adaptive, open-label, dose finding phase 1/2 trial, a total of 47 heavily pre-treated patients with ITP with a median of 6 prior therapies have been enrolled thus far, with a median follow-up of 18 weeks.

Data from this trial are being presented at a virtual session of the European Hematology Association (EHA).

The primary end point for this trial was the proportion of patients able to achieve 2 or more consecutive platelet counts, separated by at least 5 days, of ≥ 50,000/μL and an increase of platelet count of ≥ 20,000/μL from baseline, without use of rescue medication.

Of the patients who started at 400 mg twice daily and had at least 12 weeks of treatment (n = 26), 50% achieved the primary endpoint (80% CI, 38-62). Moreover, in the total patient population (n = 47), the primary end point was met by 43% of patients (80% CI, 34-52), irrespective of dose and duration of treatment.

Thus far, rilzabrutinib has been well-tolerated whether given as a monotherapy or with allowed concomitant ITP therapy (thrombopoietin receptor agonists and corticosteroids), with no reported treatment related bleeding or thrombotic events. Even further, related treatment emergent adverse events (AEs) were reported in 21 patients (45%) and were all grade 1 or 2.

“Rilzabrutinib treatment at 400 mg twice daily led to both a rapid response detectable at the first platelet measurement (day eight), and a durable response. These results are significant not only for the speed of onset and sustainability of response, but also for the heavily pretreated nature of the population in which these results were seen,” David Kuter, MD, director of Clinical Hematology at Massachusetts General Hospital, professor of Medicine at Harvard Medical School, and the trial’s principal investigator, said in the release. “It is also important to note that rilzabrutinib continues to be well tolerated and achieved significant reliable responses across subgroups at all doses and treatment times.”

Of note, these results are preliminary in nature and may vary as patients progress in the trial and as additional patients may be enrolled. A complete analysis of the trial will be presented at a future medical conference.

ITP is characterized by immune-mediated platelet destruction and impairment of platelet production, leading to downstream thrombocytopenia, a predisposition to bleeding, and adverse impact on patient quality of life. According to the National Organization for Rare Disorders, the incidence of ITP among adults in the US is estimated to be 3.3 per 100,000 adults per year.2 Moreover, worldwide, it is estimated that there are well over 200,000 people affected by ITP.


1. Principia Presents Updated Positive Data of Rilzabrutinib for Immune Thrombocytopenia in Ongoing Phase 1/2 Trial [news release]. South San Francisco, California. Published June 12, 2020. Accessed June 18, 2020.

2. NORD. Rare Disease Database: Immune Thrombocytopenia. NORD website. Published 2019. Accessed June 18, 2020.

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