PS1491 PLATELET KINETICS IN PATIENTS WITH CHRONIC IMMUNE THROMBOCYTOPENIA TREATED WITH THROMBOPOIETIN RECEPTOR AGONISTS

Abstract

Background:Chronic immune thrombocytopenia (ITP) is characterised by antibody‐mediated platelet destruction, shortened platelet survival (PS) and impaired platelets production. Platelet kinetic study (PKS) assesses in vivo the mean PS, platelet production and the platelet sequestration site. Thrombopoietin receptor agonists (TPO‐RA) increase platelets counts (PC) in majority of chronic ITP patients. Moreover, some patients could retain stabile response after TPO‐RA discontinuation, which is attributed to the immunomodulatory effects of the drugs. Addressing this issue only a few studies have been done assessing the effect of TPO‐RA on PKS parameters.Aims:To evaluate the effects of TPO‐RA on PKS parameters.Methods:Ten patients with chronic ITP, median age 55.3 years (range 12–72), gender (f: n = 7, m: n = 3), splenectomised 6/10, were treated with TPO‐RA (eltrombopag, n = 7, romiplostim, n = 3). Response was assessed according to the criteria of the International Working Group (IWG) on ITP. Autologous 111Induim‐oxinate‐labeled PKS were performed in all patients before and 5 months after TPO‐RA therapy initiation.Results:A good treatment response was achieved in 8/10 of patients (eltrombopag, n = 6, romiplostim, n = 2). Two refractory patients were treated with TPO‐RA and low dose prednisolone. Baseline median parameters were as follows: PC 6.5x109/L (range 1–17), PS 0.5 days (range 0.1–1.6, normal: 7–10), platelet production ratio 0.65 (range 0.01–3.2, normal 1 ± 0.2), platelet turnover 30875 Plt/μL/day (range 1731–103500). The post−treatment PKS showed significantly higher median PC of 62.5x109/L (range 5–501) (p = 0.013) and median platelet production ratio of 1.8 (range 0.5–37.9) (p = 0.05). However, median PS of 0.7 days (range 0.1–2.9) (p = 0.09), as well as platelet turnover of 58471.5 Plt/μL/day (range 2800–462236) (p = 0.086) and platelet destruction site remained unaltered. It is of note that two refractory patients (N08 and N010 in table) increased their platelet production (platelet production ratio and platelet turnover), while their PS remained reduced. It is of note that there was no clear correlation between PC and PS. Nevertheless, PC correlated only with platelet turnover prior (p = 0.006) and after TPO‐RA therapy (p = 0.029).Summary/Conclusion:Our prospective study in which PKS was performed initially and during TPO‐RA therapy suggests that TPO‐RA could increase PC by augmented production. Further studies on larger cohorts are needed to confirm this idea.image