Long-term safety and efficacy of fostamatinib in Japanese patients with primary immune thrombocytopenia.

Fostamatinib had superior efficacy to a placebo and acceptable safety profiles for at least 1 year in a phase 3 study of Japanese patients with primary immune thrombocytopenia. Here, we report the 3-year safety and efficacy of fostamatinib in that study. Data from 33 patients who received at least one dose of fostamatinib were analyzed. A platelet response > 50,000/µL (at two consecutive visits at least 28 days apart while receiving fostamatinib) was achieved in 16 patients (48%). The median total duration of a platelet response > 50,000/µL was 589 (range: 106-1003) days. Gastrointestinal disorders, such as diarrhea, hypertension, and hepatic enzyme elevation, were the most common fostamatinib-related adverse events. Most events occurred within 12 weeks of treatment. No thromboembolisms, treatment-related infections, or moderate or severe treatment-related bleeding events were observed. In summary, this extension study of a clinical trial found a sustained platelet response without new safety signals during 3-year treatment with fostamatinib.