Six Month Treatment of Low Dose Eltrombopag Is Efficacious in Japanese Patients with Refractory Chronic Immune Thrombocytopenic Purpura (ITP).

Eltrombopag (PROMACTA^®, GlaxoSmithKline) is the first non peptide, oral thrombopoietin receptor agonist which promotes the differentiation and proliferation of megakaryocytes and increases platelet counts. This study is a randomized study comprising a double-blind (DB), placebo (PBO)-controlled phase, followed by an open-label (OL) phase in previously treated Japanese patients with chronic ITP and platelet counts <30Gi/L. Since eltrombopag exposure has been reported to be 70% higher in East Asian patients with ITP as compared to Caucasian patients and given the chronic nature of the disease state, the lower initial dose of 12.5mg/day was used in this study.

In the DB phase, patients were randomized into one of two treatment groups to receive either an initial dose of 12.5mg of eltrombopag or matching PBO once daily. A dose increase was allowed at Day 22 based on individual platelet count. For each patient, primary data up to Week 6 were frozen and the treatment assignment was unblinded at Week 7 before entering into the OL phase. The primary endpoint of the DB phase was to compare the proportion of patients achieving a platelet count of ≥50Gi/L and ≤400Gi/L after 6 weeks of eltrombopag or PBO. All patients completing the DB phase progressed to the OL phase. In the OL phase, patients who had received eltrombopag during the DB phase continued to receive eltrombopag for up to 26 weeks with dosage (12.5, 25 or 50mg/day) based on the individual platelet count. Patients who had received PBO during the DB phase initiated treatment with 12.5mg of eltrombopag and received eltrombopag for 26 weeks with dosage (12.5, 25 or 50mg/day) based on the individual platelet count. The primary efficacy endpoint of the long-term OL phase was to assess the ability of eltrombopag to elevate and maintain platelet counts in a target range (50-400Gi/L) during 6 months of treatment. Bleeding symptoms were also assessed subjectively and objectively at each visit. Blood samples were collected to describe the PK profile of eltrombopag.

Of 23 patients randomized, 16 had undergone splenectomy, 17 had received H. pylori eradication and 19 were receiving concomitant ITP medication at baseline. DB Phase: 23 patients were randomized to receive 6 weeks of once daily eltrombopag (n=15) or matching PBO (n=8). By Week 3, 5 of 15 (33.3%) patients receiving 12.5mg eltrombopag achieved platelet counts >50Gi/L. Three of the responders had platelet counts ≥100Gi/L at Week 3. At the end of the Week 6, 9 of the 15 patients (60.0%) receiving eltrombopag were responders (platelet count 50-400Gi/L). Three of these patients were receiving 12.5mg and the remaining 6 were receiving 25mg. All PBO patients failed to achieve a response at any point during the 6 weeks. Long-term OL Phase: During the first 3 weeks when all patients received 12.5mg of eltrombopag, 21.7% of patients achieved a platelet response of ≥50Gi/L. From Day 22 onwards a greater proportion of patients (47.8-69.6%) achieved platelet counts within the target range of 50-400Gi/L. Over the initial 3 week period a gradual rise in median platelet counts was observed and a marked increase in the median platelet count was observed from Day 22. From Day 36 until Week 26 the median platelet count was consistently within the target range of 50-400Gi/L. Eltrombopag therapy was associated with a consistent reduction in the proportion of patients with bleeding. 36.8% (7/19) had a reduction in concomitant ITP medication (corticosteroids) during the 6 months.

Adverse events (AE) were reported in 22 out of 23 patients throughout the study. Nasopharyngitis was the most common AE (43%). One patient receiving eltrombopag developed a serious AE (transient ischemic attack of mild severity, considered related to study medication by the investigator) on day 10 and was withdrawn from the study. The AEs were mostly mild to moderate. There was a linear relationship between eltrombopag dose and exposure.

Six month treatment of low dose eltrombopag with an initial dose of 12.5mg up to a maximum dose of 50mg increased platelet counts and reduced bleeding and the use of concomitant ITP medication in Japanese patients with refractory ITP. The higher eltrombopag exposure in Japanese patients than in Caucasian patients may explain the equivalent efficacy at lower dosages of eltrombopag. Eltrombopag was well-tolerated and is an important new treatment option for patients with chronic ITP.

Miyakawa:GlaxoSmithKline: Consultancy; Nissan Chemical Industries: Research Funding; Shionogi: Honoraria; Ono Pharmaceutical: Honoraria. Ikeda:Daiichi-Sankyo: Research Funding; Tanabe-Mitsubishi: Research Funding; Chugai: Research Funding; Bayer: Research Funding; Daiichi-Sankyo: Honoraria; Bayer: Honoraria; Sanofi-Aventis: Honoraria; Takeda: Honoraria; GlaxoSmithKline: Honoraria; Kaken: Honoraria; Sumitomo: Honoraria; Sanofi-Aventis: Membership on an entity's Board of Directors or advisory committees; Boehringer: Membership on an entity's Board of Directors or advisory committees. Koh:GlaxoSmithKline: Employment. Katsura:GlaxoSmithKline: Employment. Kanakura:GlaxoSmithKline: Consultancy; Kyowa Hakko Kirin: Research Funding; GlaxoSmithKline: Research Funding.