Safety and Efficacy of Extended Treatment with Eltrombopag in Adults with Chronic Immune Thrombocytopenia (ITP) From June 2006 to February 2011,

Eltrombopag is an oral, nonpeptide thrombopoietin receptor agonist approved for treatment of chronic immune thrombocytopenia (ITP). In 6-week, and 6-month, placebo-controlled trials, eltrombopag safely increased platelets and reduced bleeding in patients (pts) with previously treated chronic ITP. EXTEND is an ongoing, open-label extension study of the safety and efficacy of long-term treatment with eltrombopag in chronic ITP pts. Methods: Pts had received eltrombopag or placebo in one of the following studies: TRA100773A or B (6-weeks), RAISE (6-months), or REPEAT (intermittent treatment). The EXTEND study was designed to: 1) identify an individual dose that increases platelets to ≥100,000/μL to support reduction of concomitant ITP medications, 2) identify a minimal dose of eltrombopag and concomitant ITP medication to maintain platelets ≥50,000/μL, and 3) evaluate long-term safety and efficacy. Pts completed the study if they completed ≥2 years of therapy and transitioned off study due to commercial availability of eltrombopag. Results: Of 301 pts enrolled, 21% (63) completed the study, 48% (143) withdrew, and 32% (95) remain on study. The most common reasons for withdrawal were adverse events (AEs, 14%), pt decision (13%), and lack of efficacy (11%). At baseline, platelet counts were ≤15,000/μL, >15,000-<30,000/μL, 30,000–50,000/μL, and >50,000/μL in 43%, 27%, 17%, and 13% of pts, respectively; 38% were splenectomized, 34% were receiving concomitant ITP medication, and 53% had received ≥3 previous ITP therapies. As of this report, 252, 215, 176, and 84 pts had been treated for ≥6 months, 1 year, 2 years, and 3 years, respectively. Twenty-three pts (8%) were treated for ≥4 years. Median duration of exposure was 121 weeks (range, 0.3–237 weeks). Overall, 88% (264/301) of pts achieved a platelet count ≥50,000/μL at least once. The proportion of pts achieving on-treatment platelets ≥50,000/μL was similar regardless of the following baseline characteristics: splenectomy vs no splenectomy (85% vs 89%); use vs no use of ITP medication (89% vs 87%); and platelet counts (<30,000/μL, 84%; 30,000–50,000/μL, 98%; >50,000/μL, 95%). Median platelet counts increased to ≥50,000/μL by week 2 and remained consistently ≥50,000/μL through week 208. The incidence of any bleeding symptoms (WHO grades 1–4) decreased from 56% at baseline to 16%, 19%, and 9% at weeks 52, 104, and 156, respectively. Clinically significant bleeding (WHO grades 2–4) decreased from 16% at baseline to 3%, 5%, and 0% at weeks 52, 104, and 156, respectively. AEs and serious AEs (SAEs) occurred in 89% (269) and 29% (86) of pts, respectively. The most frequent AEs were headache (27%), nasopharyngitis (24%), and upper respiratory tract infection (21%). Forty pts (13%) had AEs leading to withdrawal; 28 (9%) had SAEs leading to withdrawal. Twenty-five thromboembolic events (TEEs) have been reported in 19 pts (6%); the incidence rate is 3.02/100 pt years (95% CI [1.82–4.71]). Observed TEEs were deep vein thrombosis (10), central nervous system ischemic events (7), myocardial infarction (5), and pulmonary embolism (3). No association has been observed with elevated platelet counts, as only 3/19 pts experienced the TEE at or closest to their maximum platelet count achieved on study. Hepatobiliary laboratory abnormalities (HBLAs) meeting drug-induced liver injury screening criteria (Center for Drug Evaluation and Research 2009 [FDA]) were reported in 34 pts (11%). None were associated with signs of liver impairment, and most (n=30) resolved either while on treatment or after discontinuation. Eight pts were withdrawn as a result of their HBLA. Two pts were diagnosed with lymphoma and none with leukemia during the 622 pt years of eltrombopag exposure during EXTEND. An independent central review of bone marrow biopsies from >100 pts treated with eltrombopag for 1–4 years, including 39 pts who had ≥2 biopsies during the study, revealed no clinically significant increase in reticulin deposition. Conclusions: Eltrombopag was effective in increasing and maintaining platelet counts ≥50,000/μL and reducing bleeding symptoms. Eltrombopag was well-tolerated during treatment of pts with chronic ITP with exposures up to 4.5 years. No new safety signals have been observed in this long-term study. Additional long-term safety data continue to be assessed, especially in terms of bone marrow reticulin, HBLAs, and TEEs.

Saleh:GlaxoSmithKline: Honoraria, Research Funding, Speakers Bureau. Cheng:GlaxoSmithKline: Speakers Bureau. Bussel:Portola: Consultancy; Eisai: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; GlaxoSmithKline: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Amgen: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Cangene: Research Funding; Genzyme: Research Funding; Immunomedics: Research Funding; Ligand: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Shionogi: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sysmex: Research Funding. Burgess:GlaxoSmithKline: Employment, Equity Ownership. Marcello:GlaxoSmithKline: Employment. Bailey:GlaxoSmithKline: Employment, Equity Ownership. Brainsky:GlaxoSmithKline: Employment, Equity Ownership.