Background: 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. Methods: 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. Results: 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. Conclusions: 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.

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Eltrombopag (EPAG) received FDA approval for treatment of refractory severe aplastic anemia (rSAA) in 2014, based on our phase I/II dose escalation trial of single agent EPAG at 50-150 mg daily over a period of 12 weeks (Olnes NEJM 2012; Desmond Blood 2014). Two observations warranted further investigation of EPAG in this unique patient population. First, cell count kinetics and lack of acute toxicities suggested that extended administration of EPAG at a fixed dose of 150mg could speed and improve response rates. Second, 19% of patients developed new cytogenetic abnormalities on EPAG, raising concerns that EPAG might promote progression to MDS/AML. We conducted a subsequent phase II study of EPAG given at a fixed daily dose of 150mg for 6 months in patients with rSAA (NCT01891994). Thirtynine patients enrolled between July 2013 and April 2017. Primary endpoint was hematologic response at 6 months. Responding participants could continue EPAG treatment. Secondary endpoints included response at 3 months and the rate of clonal cytogenetic evolution. Nineteen of 39 (49%) patients met criteria for hematologic response at 6 months. Of these, 5/19 (26%) patients would have been deemed nonresponders at 3 months of treatment. EPAG was continued in 18 patients on the extension arm. EPAG was discontinued for robust response in 13/18 (72%) after a median duration of drug administration of 12 months (6-27.5 months). EPAG was re-initiated for relapse in 3/13 patients, and all 3 recovered response. At median follow up of 6 months (range 2 - 39 m), 6/39 patients (15%) developed marrow cytogenetic abnormalities, a rate comparable to our previous cohort. Given the similar rates of response and clonal evolution in our two consecutive studies, we analyzed the relationship between outcomes and cytogenetic progression for all patients (n=83) at up to 8 years of follow-up. Sixteen of 83 (18%) patients clonally evolved (Table 1). Clonal evolution was an early event after EPAG initiation. Evolution occurred within 6 months in 13/16 evolvers (81%), and in 6/6 evolvers with high risk chromosome 7 abnormalities (5/6 within 3 months). The frequency of high risk clonal evolution 24 months post intervention is comparable to historic controls with rSAA. However, direct temporal comparisons of evolution events are limited by differences in the sequence of cytogenetic tests. Nonchromosome 7 cytogenetic abnormalities were often transient, and not associated with dysplasia. Two evolvers continued EPAG off the rSAA protocol and cytogenetics normalized (UPN 71,14). The acquisition and selection of somatic mutations, particularly of myeloid candidate genes recurrently mutated in MDS/AML, has been proposed to be an initiating step in clonal evolution. We performed whole exome sequencing (WES) on samples obtained pre-EPAG treatment and at the primary response endpoint and/or time of clonal evolution in 21 responding patients and in 11 patients with cytogenetic evolution. Candidate gene mutations were detected in patients who responded (6/21) and in those with cytogenetic evolution (4/11). Clonal hematopoiesis without an identifiable driver mutation was common. In post-EPAG samples, additional myeloid candidate gene somatic mutations were detected in 2 cytogenetic evolvers and in 4 responding patients, all at low variant allele frequencies (VAF) that were close to the 2.5% detection threshold. There was no significant change in VAF in either candidate or in non-candidate genes in responders and in cytogenetic evolvers. Only one early cytogenetic evolver (UPN 01) showed an expansion of mutated clones (SETBP1 and RUNX1), from VAF of 5% to 40%, when 80% of bone marrow metaphases showed chromosome 7q deletion. In summary, extended administration of EPAG at a fixed dose of 150 mg daily for 6 instead of 3 months induces additional responses in a subgroup of patients with rSAA. After EPAG was discontinued, most patients maintained durable robust responses. The temporal relationship between clonal evolution and drug exposure suggests that in a subgroup of patients, EPAG may promote expansion of dormant pre-existing clones with an aberrant karyotype. No clinical or laboratory findings prior to therapy, including WES, predicted response or risk of clonal evolution. Careful monitoring of refSAA patients treated with EPAG is indicated, particularly in the first 6 months of treatment. (Figure Presented).

While studies have explored the feasibility of switching between various thrombopoietin receptor agonists in treating immune thrombocytopenia (ITP), data on the switching from eltrombopag to hetrombopag remains scarce. This post-hoc analysis of a phase III hetrombopag trial aimed to assess the outcomes of ITP patients who switched from eltrombopag to hetrombopag. In the original phase III trial, patients initially randomized to the placebo group were switched to eltrombopag. Those who completed this 14-week eltrombopag were eligible to switch to a 24-week hetrombopag. Treatment response, defined as a platelet count of ≥ 50 × 109/L, and safety were evaluated before and after the switch. Sixty-three patients who completed the 14-week eltrombopag and switched to hetrombopag were included in this post-hoc analysis. Response rates before and after the switch were 66.7% and 88.9%, respectively. Among those with pre-switching platelet counts below 30 × 109/L, eight out of 12 patients (66.7%) responded, while eight out of nine patients (88.9%) with pre-switching platelet counts between 30 × 109/L and 50 × 109/L responded post-switching. Treatment-related adverse events were observed in 50.8% of patients during eltrombopag treatment and 38.1% during hetrombopag treatment. No severe adverse events were noted during hetrombopag treatment. Switching from eltrombopag to hetrombopag in ITP management appears to be effective and well-tolerated. Notably, hetrombopag yielded high response rates, even among patients who had previously shown limited response to eltrombopag. However, these observations need to be confirmed in future trials.

This phase III, randomized, placebo-controlled study conducted in three stages (6-week, randomized, placebo-controlled stage 1; 24-week, open-label stage 2; and continuous extension stage 3) assessed the long-term efficacy and safety of eltrombopag use in Chinese patients with chronic immune thrombocytopenia (ITP). This article presents the results from stage 2. Overall, 150 patients (placebo-eltrombopag [P-E], 50; eltrombopag-eltrombopag [E-E], 100) received open-label eltrombopag. The median platelet count was maintained between 41 × 109/L and 80 × 109/L. Most patients in both groups (P-E, 90.0%; E-E, 81.8%) achieved platelet counts ≥30 × 109/L and ≥2 times the baseline platelet count at least once with eltrombopag treatment. Overall, 32% of patients achieved platelet counts ≥50 × 109/L in ≥75% of platelet count assessments. Both groups showed a decreased tendency to infrequent bleeding and clinically significant bleeding events during stage 2 compared with baseline. Among patients who received ≥1 ITP medication at baseline, 70.4% in the P-E group and 40.8% in the E-E group reduced or permanently stopped ≥1 of their ITP medications. The stage 2 results further demonstrated a sustainable long-term efficacy and good tolerability of eltrombopag with a favorable benefit-risk ratio in Chinese chronic ITP patients.Trial registration: Clinicaltrials.gov NCT01762761. Registered 8 January 2013, https://clinicaltrials.gov/ct2/show/NCT01762761.

PURPOSE:

This study characterized the population pharmacokinetic (pop-PK) and PK/pharmacodynamic (pop-PK/PD) properties of eltrombopag and evaluated platelet count (PLTC) response to different eltrombopag dosages through simulations in Chinese adult patients with chronic primary immune thrombocytopenia (cITP).

METHODS:

Pop-PK and pop-PK/PD models were developed from Chinese patients with cITP. Model-based simulations were then performed to predict PLTC response.

FINDINGS:

The pop-PK properties of eltrombopag were described by a 2-compartment model with first-order absorption and elimination and absorption lag time. Steady-state exposure in these Chinese patients was ~55% greater than that in non-East Asian patients. The pop-PK/PD properties of eltrombopag were described by a model with 4 transit compartments where the increase in platelet production rate was linearly related to the plasma eltrombopag concentration. Eleven percent of the patients were identified as nonresponders to eltrombopag. Simulations showed that ~70% to 80% of steady-state PLTC response was achieved at week 2, and the percentages of patients who achieved a PLTC of 50 to 150 × 10(9) cells/L were comparable between weeks 2 and 6 with 12.5-, 25-, 50-, and 75-mg once-daily dosing. The 25-mg once-daily dosage was associated with a more balanced response than were the 12.5-, 50-, and 75-mg once-daily dosages with regard to efficacy (percentages of patients with PLTC 50-150 × 10(9) cells/L, 27% vs 20%, 30%, and 30%, respectively) and the risk for thrombocytosis (percentages of patients with PLTC >250 × 10(9) cells/L, 4% vs 1%, 10%, and 16%). Simulations of PLTCs with the dose-titration regimen showed that ≥42% of patients achieved a PLTC 50 to 150 × 10(9) cells/L at week 6 or later, compared with ≤30% when the 12.5-, 25-, 50-, and 75-mg once-daily fixed doses were given. No more than 5% of patients who underwent dose titration had a PLTC >250 × 10(9) cells/L throughout 24 weeks of treatment, compared with 3%, 7%, 16%, and 24% when the once-daily fixed doses of eltrombopag were given.

IMPLICATIONS:

The pop-PK and pop-PK/PD properties of eltrombopag in these Chinese adult patients with cITP were adequately characterized in the present analyses. The modeling and simulation results support the eltrombopag dose-titration regimen, with 25 mg once daily as a starting dosage and a 2-week titration interval, in Chinese patients with cITP.

A open-label, multi-center 2-year safety study to ascertain the baseline levels of bone marrow fibers in previously treated adults with chronic immune (idiopathic) thrombocytopenic purpura (ITP) and to evaluate the long-term effect of eltrombopag on bone marrow fibers. The study will also describe the long-term safety and tolerability of oral eltrombopag treatment in subjects with chronic ITP.

To investigate the efficacy of eltrombopag for the treatment of thrombocytopenia in patients with chronic hepatitis C, a phase II, single-arm, open-label study with a 9-week pre-antiviral phase was conducted, followed by a 48-week antiviral phase and a 24-week follow-up phase. The proportion of patients who achieved a platelet count threshold, the proportion of patients who maintained a platelet count >50,000/μl, sustained virological response (SVR) rates and safety parameters were evaluated. Of the 45 enrolled patients (median age, 59 years; median platelet count, 63,000/μl; 98% with Child-Pugh class A), 43 (96%) achieved the platelet count threshold during the pre-antiviral phase. A total of 13 patients (29%) experienced ≥1 adverse event (AE), of which headache and vomiting were the most common, and 41 patients (mostly receiving eltrombopag 12.5 mg or 25 mg) entered the antiviral phase, of which 36 (88%) maintained the platelet count threshold; no patient platelet count decreased below 25,000/μl. Nine patients (22%) achieved an SVR at the 24-week follow-up. Grade ≥3 AEs occurred in 25 patients (61%). A total of 8 serious AEs occurred in five patients (12%). No mortality, thromboembolic events (TEEs), or cataract progression were reported. Eltrombopag increased the platelet count in chronic hepatitis C virus-infected patients with cirrhosis and thrombocytopenia and enabled them to initiate and complete interferon-based antiviral therapy (NCT01636778; first submitted: July 05, 2012).

A 55-year-old female with stage IVA follicular lymphoma in third complete remission underwent allogeneic peripheral blood stem cell transplantation. Neutrophil engraftment was achieved on day +18; however, platelet counts remained below 10 × 10(3)/µL, necessitating transfusions twice a week for more than 3 months. Bone marrow showed a decreased number of megakaryocytes with hypolobulated nuclei. No graft versus host disease, viral infection, or disease relapse was observed. Furthermore, severe thrombocytopenia below 5.0 × 10(3)/µL refractory to transfusion appeared on day +240 after influenza virus infection. Treatments with intravenous immunoglobulin, romiplostim, and rituximab were administered without any recovery. Subsequently, eltrombopag was initiated on day +443, after which platelet counts rose gradually and continued to rise above 20 × 10(3)/µL after 10 weeks of administration. The serum thrombopoietin (TPO) level was markedly elevated, and anti-TPO receptor (TPOR) antibody was detected in the patient's serum. Anti-TPOR antibody may play an important role in some cases of prolonged thrombocytopenia after allogeneic hematopoietic stem cell transplantation with unknown etiology, and eltrombopag could be a novel therapeutic option for such cases.

A double-blind, randomized, placebo-controlled phase I/II study to evaluate the safety and tolerability of eltrombopag olamine, a thrombopoietin receptor agonist, administered for 6 months as oral tablets once daily in adult subjects with advanced MDS, sAML/MDS, or de novo AML. Study medication may be increased up to 300 mg (150 mg maximum dose for East Asian subjects), based upon individual platelet counts and bone marrow blast counts.