Platelet Kinetics in Idiopathic Thrombocytopenic Purpura Patients Treated with Thrombopoietin Receptor Agonists

Aim: Thrombopoietin receptor agonists (Tpo RA) increase platelet counts in the majority of chronic autoinnmune thrombocytopenia (idiopathic thrombocytopenic purpura; ITP) patients. It is unknown whether this treatment may also improve platelet survival (PS) in these patients. Methods: In order to determine platelet survival (PS), autologous platelets were labeled with In-111 oxine and retransfused in six patients under treatment with Tpo RA (romiplostim n = 3; eltrombopag n = 3). Results: Stable platelet counts of greater than 100 x 10(3)/mu l were observed in all 6 patients. Platelet survival was decreased in all cases (mean 2.10 days; range 0.13-3.73 days). No correlation was found between platelet count and PS. Similarly, there was no significant relationship between platelet turnover and platelet count. However, a high platelet turnover, exceeding 25 or three times the norm was observed in 2 patients who presented the lowest PS (0.13 or 0.83 days). Two patients had a moderately shortened PS (1.91 or 2.42 days), and, correspondingly, a moderately increased platelet turnover rate (63,072 or 72,872 platelets/mu l/day). Conclusion: These results indicate that Tpo RA may not only overcompensate platelet destruction in ITP, but may interfere with other mechanisms, which, in some cases, results in a reduced platelet destruction rate.