Dexpramipexole depletes blood and tissue eosinophils in nasal polyps with no change in polyp size

Objective Chronic rhinosinusitis with nasal polyps (CRSwNP) and eosinophilia is a disease of the upper respiratory tract for which few therapies are available. Because the oral investigational drug dexpramipexole serendipitously decreased blood eosinophils in amyotrophic lateral sclerosis studies, we assessed its safety, eosinophil‐lowering activity, and preliminary clinical efficacy in patients with CRSwNP and eosinophilia. Methods Sixteen subjects with CRSwNP, absolute eosinophil count (AEC) ≥ 0.300 × 109/L, and polyp tissue eosinophils were evaluable for efficacy in a 6‐month open‐label, multi‐center study of dexpramipexole 150 mg twice daily. The coprimary endpoints were change in AEC and change in total polyp score (TPS) from baseline to month 6, with additional clinical and histologic endpoints assessed. Results Thirteen of 16 subjects completed 6 months of dexpramipexole treatment. Geometric mean baseline AEC was 0.525 ± 0.465 eosinophils × 109/L and decreased to 0.031 ± 0.019 after 6 months of dexpramipexole treatment, a 94% reduction (P