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Thrombopoietin receptor agonists in ITP
and substantial thrombocytopenia in affected recipients. Importantly, neither romiplostim nor eltrombopag are rec- ommended to be used in pregnancy; however, there are limited case reports in which the use of these agents in pregnant women with difficult ITP appeared to be safe.
Future treatments for immune thrombocytopenia and the role of thrombopoietin receptor agonists
The two TPO-RA licensed for use in ITP are now both licensed for use after one year from diagnosis after failure of corticosteroids, further consolidating their position as the mainstay for second-line therapy in ITP. However, many other agents are currently under development, at various stages of clinical testing, or are being considered for registration. Among these, fostamatinib, an inhibitor of spleen tyrosine kinase (syk) has an overall response rate of almost 50% with continued treatment, and an 18% rate of stable responses in heavily pretreated ITP patients.85 This agent was licensed in the US in 2018 for treatment of
chronic ITP in adults. Several blockers of FcRn have entered trials in adults with persistent and chronic ITP; at least two (rozanolixizumab and ARGX-117) have com- pleted phase II studies.86 The mechanism is a dramatic increase in IgG turnover as a result of inhibition of IgG recycling; not only “normal” but also IgG autoantibody levels decrease markedly.87 Preliminary results are encour- aging but efficacy and toxicity need to be better defined in phase III studies. It remains to be seen how these agents will influence the future role of TPO-RA.
Conclusion
Romiplostim and eltrombopag are well tolerated and effective therapies for ITP with acceptable toxicity. Both agents increase the platelet count in up to three-quarters of patients. Ten years after their introduction, available evi- dence from short- and long-term and registry-based studies confirm the general safety of chronic long-term use of these medications, as well as persistent efficacy in most patients.
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