Thrombopoietin Receptor Agonists (TPO-RA) are novel treatment modalities for patients with refractory Primary Immune Thrombocytopenia (ITP), but only few data are available for long-term effects of these drugs. In this observational study, long-term effects and adverse effects including evaluation of bone marrow biopsies done at fixed intervals will be recorded from ITP patients treated with TPO-RA.