FDA Approves Fostamatinib for Chronic Immune Thrombocytopenia

The US Food and Drug Administration (FDA) announced the approval of fostamatinib disodium hexahydrate (Tavalisse, Rigel) for the treatment of thrombocytopenia in adults with chronic immune thrombocytopenia (ITP) who have had an insufficient response to a previous treatment.

The only other approved therapies for ITP are steroids, blood platelet productions boosters, and splenectomy, but there remained a significant need for additional options, as many patients achieve benefit from them.

"Chronic ITP is challenging to treat because the heterogeneity of the disease makes it difficult to predict how an individual patient will respond to available treatments and not all patients can find a treatment that works well for them," James Bussel, MD, the professor emeritus of pediatrics at Weill Cornell Medicine, said in statement. "The FDA approval of fostamatinib arms physicians with a new treatment option, which works via a novel mechanism."

Bussel, who served as a consultant and paid member of the advisory board for Rigel Pharmaceuticals, Inc, was also the principal study investigator on the FIT Phase 3 program, consisting of 2 phase 3 clinical trials which the FDA utilized to make its decision.

The data in the New Drug Application included 163 patients with ITP and platelet counts <30,000/µL—as well as a safety database of more than 4600 patients across other indications in which fostamatinib has been evaluated&mdash;and randomized them 2:1 based on prior splenectomy and baseline platelet count (<15,000/µL vs. ≥15,000/µL) to receive fostamatinib 100 mg or placebo twice daily for 24 weeks.

The findings revealed a response rate of 29% for those on the therapy compared to 2% with placebo (P <.001). A stable response (SR), defined as a platelet count ≥50,000/μL at 4 of 6 biweekly visits through weeks 14-24 without rescue treatment occurred in 18 on fostamatinib compared to just 1 on placebo (P= .007), while an intermediate response (IR), defined as at least 2 consecutive biweekly platelet counts ≥50,000/μL without rescue treatment, occurred in 11 and 0 patients, respectively (P <.001).

The median platelet counts at 24 weeks of follow-up were 95,000/µL in the SR group, 49,000/µL in the IR group, and 20,500/µL in the non-responders. In total, 54% of fostamatinib-treated patients had increased platelet levels ≥20,000/μL, compared with 29% of patients receiving placebo (n=14/49; P = .005).

"People living with chronic ITP often feel they have an invisible disease—one that can not only impact [the] quality of life, but also be life-threatening," said Caroline Kruse, the executive director of the Platelet Disorder Support Association, a patient advocacy organization dedicated to ITP, in a statement. "That's why we encourage members of our community to learn about their disease, understand treatment strategies, and seek support so that they can advocate for their best care. The availability of a new treatment option provides the ITP community with more choices."