Fostamatinib therapy may provide durable long-term responses for adult patients with immune thrombocytopenia (ITP), according to a recent report in the American Journal of Hematology.
Phase 3 trials described in this report included 2 randomized, double blind trials in adult patients with long-term ITP (ClinicalTrials.gov Identifiers: NCT02076399 and NCT02076412) and a follow-up, open label extension study (ClinicalTrials.gov Identifier: NCT02077192).
Patients with ITP were treated with either fostamatinib (102 patients total) or placebo (48 patients total) during the randomized trials. Most patients (123/150) then participated in the open label extension study, where they received fostamatinib as part of a long-term evaluation of efficacy and safety. Fostamatinib dosage was either 100 mg or 150 mg twice daily based on study design and patient responses. Fostamatinib was given to 146 patients overall.
Endpoints of each study included overall and stable response rates. Overall response was defined as achieving a platelet count of at least 50,000/mL at least once within the first 3 months of fostamatinib treatment and without rescue treatment. Stable response consisted of achieving this platelet count for a set number of visits at intervals according to trial phase.
The median time on fostamatinib was 6.7 months, with 67% of patients remaining on fostamatinib for 6 or more months. Overall response was achieved by 44% of patients on fostamatinib, who had a median platelet count of 63,000/mL and median duration of response of more than 28 months. Stable response was achieved by 18% of patients, who had a median platelet count of 89,000/mL and median duration of response of more than 28 months.
At data cutoff, 49 patients remained in the open label extension study. Among all patients given fostamatinib, 31% discontinued because of lack of response and 16% discontinued because of adverse events. Adverse events were mild for 21% of patients and moderate for 41% of patients. Diarrhea, abnormal liver function tests, hypertension, epistaxis, and nausea were among the most common adverse events.
The authors concluded that fostamatinib demonstrated feasibility and durability of stable and overall platelet responses but recommended follow-up studies to further evaluate mechanisms and patterns of treatment response.
- Bussell JB, Arnold DM, Boxer MA, et al. Long-term fostamatinib treatment of adults with immune thrombocytopenia (ITP) during the phase 3 clinical trial program [published online February 19, 2019]. Am J Hematol. doi: 10.1002/ajh.25444