FDA Approves Mepolizumab for Hypereosinophilic Syndrome


The FDA has approved mepolizumab (Nucala; GSK) as the first biologic treatment of hypereosinophilic syndrome.


The FDA has approved mepolizumab (Nucala; GlaxoSmithKline) for the treatment of adult and pediatric patients aged 12 and older with hypereosinophilic syndrome (HES) for at least 6 months without an identifiable non-hematologic secondary cause.

HES is a rare and under-diagnosed disorder; therefore, its prevalence in the United States and globally is difficult to estimate. However, Dr. Hal Barron, chief scientific officer and president R&D, estimated that the disease affects approximately 5000 patients in the United States. “Today’s approval gives these patients access to a biologic treatment for the first time and demonstrates our commitment to maximizing Nucala’s impact on eosinophil-driven diseases,” Barron continued.

Individuals with HES experience an overproduction of eosinophils, a type of white blood cell, which can lead to inflammation and organ damage. Maintenance of the levels of eosinophils can improve these results, but if left untreated, HES symptoms can become worse and life-threatening.

“Patients with HES often suffer from debilitating flares of their disease,” said D. Gerald Gleich, MD, allergist, immunologist, and a HES expert. “Reducing them is an important treatment goal. For the first time, we now have a biologic treatment option to offer appropriate patients with this complex disease.”

Mepolizumab is the first-in-class monoclonal antibody that targets interleukin 5 (IL-5); researchers believe that the drug functions by preventing IL-5 from binding to its receptor on the surface of eosinophils, reducing blood eosinophils to normal levels. It has been studied for numerous eosinophilic indications and has been approved under the Nucala brand in the United States, Europe, and more than 20 other markets.

The approval was based on a 32-week, randomized, double-blind, placebo-controlled, phase 3 study that included 108 patients 12 years and older with uncontrolled HES that aimed to investigate the efficacy and safety of subcutaneous mepolizumab 300 mg. Mepolizumab was administered to patients every 4 weeks and compared with placebo.

The results showed 50% fewer patients experienced a HES flare when treated with mepolizumab, compared with placebo, when added to standard-of-care treatment over the 32-week study period, according to the study.

“HES can take many years to diagnose and most patients go through a long and frustrating journey that continues even after the diagnosis is confirmed as treatment roadmaps are often unclear and limited,” said Mary Jo Strobel, executive director, American Partnership for Eosinophilic Disorders (APFED). “APFED welcomes this approval of Nucala for HES as it gives our community hope.”


  1. FDA approves Nucala as the first and only biologic treatment for Hypereosinophilic Syndrome (HES). News Release. GSK; September 25, 2020. Accessed September 25, 2020. https://www.gsk.com/en-gb/media/press-releases/fda-approves-nucala-as-the-first-and-only-biologic-treatment-for-hypereosinophilic-syndrome-hes/.

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