Arena determined to press on despite phase II fail

If history has taught us anything it is that moving from phase II to phase III on questionable data rarely ends well. Arena Pharmaceuticals is confident it can buck the trend. Yesterday, the group reported that the phase IIb Advise trial of etrasimod missed its primary endpoint of percent change versus placebo on the eczema area and severity index (EASI) at week 12. Arena pinned the miss on “unwarranted drug interruption” in the 2mg arm after one study site incorrectly halted treatment following lower lymphocyte counts in 19% of patients. A post-hoc analysis of those who had completed treatment did find a significant difference on this measure, Arena claimed, while a secondary endpoint, change on the vIGA scale, also succeeded, although the miss on the primary endpoint surely renders these finding exploratory. The company plans to push into phase III trials using vIGA measure as the primary endpoint. Only $151m of etrasimod’s forecast $1.09bn sales in 2026 come from atopic dermatitis, according to EvaluatePharma, so Arena’s 24% share price fall probably also reflects concerns around the lymphocyte count signal, and what that means for etrasimod’s main indication of ulcerative colitis. Phase III data are due in this indication in 2022.

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