Long-Term Safety and Efficacy of Eltrombopag in Adults with Chronic Immune Thrombocytopenia (ITP): Report of up to 5.5 Years of Treatment in EXTEND.

Eltrombopag is an oral thrombopoietin receptor agonist approved for treatment of chronic ITP. Eltrombopag safely increased platelets and reduced bleeding in 6-week and 6-month placebo-controlled trials in patients 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 patients who completed a previous eltrombopag study.

Patients had received eltrombopag or placebo in a prior study. Eltrombopag was started at 50 mg and titrated to between 75 and 25 mg daily or less often, based on platelet counts. Patients were considered to have completed EXTEND if they had received ≥2 years of therapy and transitioned off due to commercial availability of eltrombopag, whether or not they continued with treatment. The study started in June 2006, and an update on long-term safety and efficacy up to February 2012 is presented.

Of 302 patients enrolled, 31% (95) completed the study, 48% (146) withdrew, and 20% (61) remain on study. The most common reasons for withdrawal were adverse events (AEs, 14%), patient decision (14%), and lack of efficacy (11%). Platelet counts at baseline were ≤15,000/μL (43%), >15,000-<30,000/μL (27%), 30,000–50,000/μL (17%), and >50,000/μL (13%); 38% were splenectomized, 33% were receiving concomitant ITP medication, and 53% had received ≥3 previous ITP therapies. 253 patients were treated for ≥6 months, 217 for ≥1 year, 176 for ≥2 years, and 59 for ≥4 years; 10 patients (3%) were treated for ≥5 years. Median duration of exposure was 121 weeks (range, 0.3–285 weeks), and median average daily dose was 51.4 mg. Overall, 85% (257/302) of patients achieved a platelet count ≥50,000/μL in the absence of rescue therapy, and 62% of patients achieved platelets ≥50,000/μL for ≥50% of on-treatment weeks. The proportion of patients achieving platelets ≥50,000/μL was similar regardless of baseline splenectomy status: splenectomy, 80% vs no splenectomy, 88%. Median platelet counts increased to ≥50,000/μL by Week 2 and remained consistently ≥50,000/μL through Week 241. The incidence of any bleeding symptoms (WHO grades 1–4) decreased from 57% at baseline to 16% at Week 52, 19% at Week 104, 12% at Week 156, and 14% at Week 208. Clinically significant bleeding (WHO grades 2–4) decreased from 17% at baseline to 4%, 5%, 0%, and 0% at Weeks 52, 104, 156, and 208, respectively. AEs and serious AEs (SAEs) occurred in 91% (275) and 29% (89) of patients, respectively. The most frequent AEs were headache (27%), nasopharyngitis (24%), and upper respiratory tract infection (22%). 43 patients (14%) were withdrawn due to AEs, 29 (10%) of which were SAEs. Twenty-five thromboembolic events (TEEs) were reported in 19 patients (6%); the incidence rate is 2.70/100 patient years (95% CI, 1.62–4.21). 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 patients experienced the TEE at or shortly after their maximum platelet count achieved on study. Hepatobiliary laboratory abnormalities (HBLAs) meeting drug-induced liver injury screening criteria (FDA Guidance for Industry Drug-Induced Liver Injury, 2009) were reported in 36 patients (12%). None were associated with signs of liver impairment, and most resolved either while on treatment or after discontinuation. Eight patients were withdrawn as a result of HBLA. An independent central pathology review of bone marrow (BM) biopsies stained for reticulin from 113 patients treated with eltrombopag for up to 4.75 years revealed no clinically relevant increase in reticulin deposition. 2 patients (2%) had maximum reticulin grade of ≥MF-2 after >24 months on treatment; neither experienced any AE or abnormality in hematologic parameters potentially related to impaired BM function.

Eltrombopag was effective in increasing and maintaining platelets ≥50,000/μL and reducing bleeding symptoms in patients with chronic ITP. Eltrombopag was well tolerated with exposures up to 5.5 years. Rates of TEE and HBLA have not increased with longer time on treatment, and analyses of BM biopsies revealed no clinically significant increase in reticulin deposition. No new safety signals were observed in this long-term study. Long-term safety and efficacy continue to be assessed.

Cheng:GlaxoSmithKline: Honoraria, Speakers Bureau. Bussel:Amgen: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding; Cangene: Research Funding; GlaxoSmithKline: Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding; Genzyme: Research Funding; IgG of America: Research Funding; Immunomedics: Research Funding; Ligand: Membership on an entity's Board of Directors or advisory committees, Research Funding; Eisai, Inc: Membership on an entity's Board of Directors or advisory committees, Research Funding; Shinogi: Membership on an entity's Board of Directors or advisory committees, Research Funding; Symphogen: Membership on an entity's Board of Directors or advisory committees; Sysmex: Research Funding; Portola: Consultancy. Burgess:GlaxoSmithKline: Employment, Equity Ownership. Bakshi:GlaxoSmithKline: Employment, Equity Ownership. Brainsky:GlaxoSmithKline: Employment, Equity Ownership, Patents & Royalties. Bailey:GlaskoSmithKline: Employment, Equity Ownership.