Rigel’s fostamatinib has low ITP market potential vs TPO mimetics despite positive Phase III with inferior superiority, GI toxicities – experts

05 Oct 2016

Rigel Pharmaceuticals' (NASDAQ:RIGL) fostamatinib disodium has a poor treatment position in the idiopathic thrombocytopenic purpura (ITP) landscape versus its main competitor, thrombopoietin (TPO) mimetics, despite statistically significant Phase III outcomes, experts agreed. They noted whilst fostamatinib will likely be a third-line option like TPO mimetics, the latter will still be preferred with a superior strong, speedy response rate.

One expert argued, however, fostamatinib's median platelet count of more than 100,000/uL may boost its use amongst the small patient proportion failing on TPO mimetics and other existing therapies.

Phase III's gastrointestinal (GI) toxicity read outs could pose an additional uptake roadblock, with some experts arguing patients may find them intolerable. They added, however, adverse event (AE)-related drop-outs are unknown, as well as the efficacy of GI treatments in ITP patients, creating uncertain safety concerns.

According to a Rigel spokesperson, fostamatinib has significant commercial potential as its unique mechanism of action (MOA), alongside robust and enduring Phase III benefits, suggest the agent may work where other treatments fail.

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