Mepolizumab Reduces Flares in Patients With Hypereosinophilic Syndrome

Eosinophil cells
Eosinophil cells

GlaxoSmithKline announced positive results from the pivotal phase 3 study of mepolizumab in the treatment of patients with hypereosinophilic syndrome (HES).

HES is a rare group of inflammatory disorders characterized by persistent eosinophilia that can potentially lead to inflammation, organ damage, and possibly death if left untreated. 

The 32-week, double-blind, placebo-controlled phase 3 study evaluated the efficacy and safety of mepolizumab vs placebo in adolescent and adult patients with severe HES (N=108), defined as ≥2 HES flares within the past 12 months and a blood eosinophil count of ≥1000 cells/µL. Patients were randomized to receive either mepolizumab 300mg every 4 weeks or placebo. The primary end point was the proportion of patients who experienced an HES flare during the 32-week treatment period.

Results showed that the study met its primary end point, with 50% fewer patients in the mepolizumab treatment arm experiencing an HES flare vs placebo when added to standard of care treatment (56% vs 28%, respectively; P =.002). Additionally, mepolizumab was found to be statistically significant for key secondary end points vs placebo, including a 66% reduction in the risk of first HES flare with mepolizumab vs placebo (HR 0.34; 95% CI 0.18, 0.67), a 66% reduction in the annualized rate of HES flares vs placebo (rate ratio 0.34; 95% CI 0.19, 0.63), and improved fatigue scores with mepolizumab vs placebo (P =.036). With regard to safety, mepolizumab was found to be consistent with its already known profile. 

“These data are very promising and should provide hope for patients affected by this rare, life-threatening condition caused by eosinophilic inflammation,” said Gerald Gleich, MD, allergist, immunologist and HES expert, University of Utah  Full study results will be submitted for future presentation at upcoming scientific meetings and in peer-reviewed publications. 

The Company plans to progress regulatory submissions in 2020. The FDA previously granted Fast Track and Orphan Drug designations to mepolizumab for HES. 

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Mepolizumab (Nucala), an interleukin-5 antagonist, is currently approved for use as an add-on maintenance treatment for patients with severe asthma with an eosinophilic phenotype. It is also indicated in the treatment of eosinophilic granulomatosis with polyangiitis

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