Primary immune thrombocytopenia (ITP) is an autoimmune bleeding disorder. Increased macrophage phagocytosis of antibody-coated platelet as well as decreased number and/or impaired function of CD4+CD25+Foxp3+ regulatory T (Treg) cells have been shown to participate in the pathogenesis of ITP. Our preclinical data revealed that chidamide, a histone deacetylase inhibitor (HDACi), could attenuate macrophage phagocytosis of antibody-coated platelets, stimulate production of natural Foxp3+ Tregs, and upregulate CTLA4 expression through modulation of histone H3K27 acetylation. The project was undertaking by Qilu Hospital of Shandong University in China. In order to evaluate the efficacy and safety of chidamide at two different dosage regimens in adult patients with refractory ITP.

In this prospective, open-label, multicenter, randomized clinical trial, refractory ITP adult patients will be enrolled from five medical centers in China. Eligible participants will be randomly assigned 1:1 to receive chidamide at either 2.5 or 5 mg twice per week. The primary endpoint is the overall response at week 12. Complete response was defined as a platelet count at or above 100×10^9/L and an absence of bleeding. Partial response was defined as a platelet count at or above 30×10^9/L but less than 100×10^9/L and at least a doubling of the baseline platelet count and an absence of bleeding. No response was defined as a platelet count of less than 30×10^9 cells per L, or less than two-times increase from baseline platelet count, or bleeding. The secondary enpoints included 6-month sustained response, time to response (TTR), duration of response, bleeding scores, health-related quality of life assessment and adverse events (AEs). This study will compare the efficacy and safety of chidamide in two different dosage regimens in adult patients with refractory.

Inclusion Criteria:

• Participant must be at least 18 years of age at the time of the screening.
• Participant may be male or female.
• Participant has a confirmed diagnosis of ITP according to the 2019 International Working Group assessment for more than 6 months at screening.
• Participant who didn't respond or relapsed after previous first-line treatment, and lack of response to rituximab, TPO agents, or splenectomy.
• Bone marrow biopsy is performed in participants over 60 years to exclude hematological malignancies.

Exclusion Criteria:

• Participant has evidence of a secondary cause of immune thrombocytopenia or to drug treatments or participant has a multiple immune cytopenia, e.g. Evan's syndrome.
• Participant with the following conditions:severe dysfunction of the heart, kidney, liver, or lung; severe immunodeficiency; malignancy; HIV; hepatitis B or C virus infection; pregnancy or lactation.