Rituximab As Second-Line Treatment For Chronic Immune Thrombocytopenia: Investigator-Initiated Clinical Trial In Japan

The American Society of Hematology guidelines recommend rituximab as second-line treatment, as well as splenectomy and thrombopoietin receptor agonists (TPO-RAs), for chronic immune thrombocytopenia (ITP). However, rituximab has not been approved for the treatment of chronic ITP in Japan. To establish chronic ITP as a new indication for rituximab, we conducted an investigator-initiated clinical trial to clarify the efficacy and safety of rituximab for Japanese patients with ITP.

This study was designed as a single-arm, multicenter phase III study. Patients diagnosed with chronic ITP who were previously treated with at least one therapy for ITP and whose platelet count was ≤ 30,000/μL were included. Patients with a past history or current hepatitis B virus, hepatitis C virus or HIV infection, who were treated with splenectomy within 12 weeks or with TPO-RA within 4 weeks were excluded. Rituximab at a dose of 375 mg/m²was intravenously infused once weekly for 4 weeks. Patients were premedicated with acetaminophen, restamin and hydrocortisone to prevent infusion reactions. Platelet counts, bleeding symptoms, and B lymphocyte counts were observed once monthly following the protocol. The primary endpoint was the proportion of patients whose platelet count was ≥ 50,000/μL 24 weeks after treatment with rituximab.

Between October 2011 and January 2013, 26 patients were enrolled in this study from 10 hospitals in Japan. Median age of the patients was 40 years and 89% were female. Baseline platelet counts were 23,000/μL. Median interval from diagnosis of ITP to commencing rituximab therapy was 5.9 years. Previous treatment of ITP was corticosteroids (69%), splenectomy (15%), TPO-RA (27%) and intravenous immunoglobulins (39%). At baseline, 58% of patients had some bleeding symptoms. Median number of previous ITP treatments was two. All patients completed the study. At 24 weeks after treatment, 30.8% (95% CI: 14.3–51.8%) of patients achieved platelet counts > 50,000/μL. Seven of eight responders demonstrated improvement until 8 weeks. Platelet count was significantly increased compared with baseline (P<0.001). No unknown severe adverse events were observed. Subgroup analyses showed that ITP duration was numerically associated with the efficacy rate (46% vs 15% for duration< median vs ≥ median, respectively). Bleeding symptoms measured with the WHO bleeding scale were improved compared with baseline.

We demonstrated the efficacy and safety of rituximab in Japanese patients with chronic ITP. The response rate was similar to that in previous reports in the US and Europe. We plan to propose that the Japanese government approve chronic ITP as a new indication for rituximab.