Statistically significant NATRON Phase III trial results for hypereosinophilic syndrome show FASENRA delayed time to first flare or worsening of disease

FASENRA also demonstrated a greater improvement in fatigue symptom relief in a single monthly dose compared to placebo

WILMINGTON, Del., November 07, 2025--(BUSINESS WIRE)--Positive full results from the NATRON Phase III trial showed AstraZeneca’s FASENRA (benralizumab) demonstrated a statistically significant delay in the time to first worsening or flare in hypereosinophilic syndrome (HES),1 a rare disease driven by elevated eosinophils.2 These data will be presented at the American College of Allergy, Asthma and Immunology (ACAAI) 2025 Annual Scientific Meeting in Orlando, Florida.

Hypereosinophilic Syndrome (HES) is a group of rare disorders characterized by persistent, significantly elevated levels of eosinophils (a type of white blood cell) in the blood and evidence of eosinophil-mediated organ or tissue damage.2 This may lead to progressive organ damage over time and if left untreated, may be fatal.2 Current treatments include glucocorticosteroids, chemotherapy medicines, tyrosine kinase inhibitors and an anti-interleukin-5 (IL-5) monoclonal antibody.2

NATRON was a Phase III trial evaluating the efficacy and safety of FASENRA in patients with HES.3 Patients were randomized to receive either a single 30 mg subcutaneous injection of FASENRA or a placebo once every four weeks.3 The trial successfully met the primary endpoint, as treatment with FASENRA delayed the time to first HES worsening/flare and significantly reduced the risk of HES worsening/flare compared to placebo by 65% (19.4% vs 42.4% events; HR 0.35; 95% CI: 0.18, 0.69; P=0.0024).1

Princess U. Ogbogu, Division Chief of Pediatric Allergy, Immunology, and Rheumatology at University Hospitals Rainbow Babies and Children’s Hospital and Case Western Reserve University, Cleveland, OH, the trial’s principal investigator, said: "From my years of treating patients with hypereosinophilic syndrome, I know first-hand how devastating HES symptoms can be, including fatigue, organ involvement and impacts on quality of life. The NATRON results suggest we have the potential to help HES patients with benralizumab, significantly reduce the risk of flares, hematologic relapse and improve fatigue severity compared to placebo with a single monthly dose regime."

Sharon Barr, Executive Vice President, BioPharmaceuticals R&D, AstraZeneca, said: "The NATRON results confirm FASENRA’s ability to address eosinophilic inflammation in difficult to treat eosinophilic-driven diseases, like HES and eosinophilic granulomatosis with polyangiitis, in addition to severe eosinophilic asthma. By sharing the full results from NATRON with the medical community today and progressing our regulatory filing, we hope to realize a future in which FASENRA helps patients with HES who currently have very limited options."

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All key secondary endpoints in the trial were also met, as treatment with FASENRA resulted in fewer proportion of patients experiencing a flare or withdrawing (22.4% vs 45.5%; odds ratio: 0.31; 95% CI: 0.14, 0.69; P=0.0033) and a 66% reduction in the annualized rate of HES flares compared to placebo: 0.41 vs 1.23 flares per year, respectively (rate ratio: 0.34; 95% CI: 0.18, 0.63; P=0.0008).1 Time to first hematologic relapse was delayed for patients on FASENRA compared to placebo (hazard ratio: 0.08; 95% CI: 0.03, 0.20; P