FDA Approves Emapalumab-Lzsg as First-Ever Treatment for Macrophage Activation Syndrome in Still Disease

The FDA has announced regulatory approval of emapalumab-lzsg (Gamifant; Sobi) for the treatment of adult and pediatric patients with hemophagocytic lymphohistiocytosis (HLH)/macrophage activation syndrome (MAS) in known or suspected Still disease, including systemic juvenile idiopathic arthritis (sJIA), with an inadequate response or intolerance to glucocorticoids or with recurrent MAS, according to a news release from Sobi.¹

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Pooled clinical data from pivotal studies, including the phase 3 EMERALD trial (NCT05001737) and NI-0501-06 (NCT03311854), solidified the efficacy and safety of emapalumab in patients with MAS in Still disease. A total of 39 patients with MAS were enrolled in the trials and received intravenous infusions of emapalumab. According to the data, 54% of participants treated with emapalumab had a complete response at week 8, while 82% achieved clinical MAS remission at week 8. Furthermore, the tolerability and safety of emapalumab were consistent with indications from prior studies, with the most common adverse events being viral infections.^1-4

Previously, the FDA accepted the biologics license application for emapalumab and granted the treatment priority review, allowing for a speedier consideration for full approval.⁴

“MAS in Still disease is a serious and potentially life-threatening complication, marked by severe hyperinflammation and, in some cases, multi-organ failure. Many patients affected by MAS—both young children and adults—face significant unmet medical needs,” Alexei A. Grom, MD, professor of pediatrics and research director of the division of rheumatology at Cincinnati Children’s Hospital Medical Center, said in the news release. “With [emapalumab] now as the first FDA-approved treatment for MAS, we have a new therapeutic option that helps control hyperinflammation and reduce our reliance on high-dose glucocorticoids.”¹

MAS is a severe complication of rheumatic diseases and occurs most frequently in Still disease. HLS/MAS is a rare, systemic disorder of interferon gamma-driven hyperinflammation, often presenting with consistently high fever, elevated ferritin, coagulopathies, and cytopenia, among others. In some cases, MAS can progress to multiple organ failure or even death. Given the lack of treatments available for patients with this condition, the approval of emapalumab—a monoclonal antibody designed to bind and neutralize interferon gamma—is poised to offer patients a new, effective therapeutic option for disease management and quality of life improvement.^1,4

Emapalumab was initially approved by the FDA in 2018 for the treatment of adult and pediatric patients with primary HLH with refractory, recurrent, or progressive disease or intolerance with conventional HLH therapy, becoming the first and only treatment approved by the FDA for that indication.^1,4

“With our expertise in primary hemophagocytic lymphohistiocytosis, we understand the urgency of managing MAS quickly to improve patient outcomes,” Guido Oelkers, CEO of Sobi, said in the news release. “[Emapalumab] is already an established therapy making a meaningful difference for patients with primary HLH, and with this approval, we are excited about the opportunity to positively impact patients affected by MAS in Still’s disease.”¹

Emapalumab is indicated for administration through intravenous infusion over 1 hour, according to Sobi. Pharmacists stand to play an outsized role in the management of patients with MAS in Still disease being treated with emapalumab for their condition. Through determining proper dosing schedules, ensuring infusions go smoothly and are effective, and identifying and managing adverse events, pharmacists are critical in the treatment process for patients in this population.¹

REFERENCES

1. Sobi. FDA approves Gamifant (emapalumab-lzsg) as first-ever treatment for adults and children with Macrophage activation syndrome in Still’s disease. News Release. Released June 28, 2025. Accessed June 30, 2025. https://www.sobi.com/en/press-releases/fda-approves-gamifantr-emapalumab-lzsg-first-ever-treatment-adults-and-children-macrophage-activation-syndrome-stills-disease-2342991

2. A Study to Investigate the Safety and Efficacy of Emapalumab, an Anti-IFN-gamma mAb in Patients With Systemic Juvenile Idiopathic Arthritis (sJIA) or Adult-onset Still's Disease (AOSD) Developing Macrophage Activation Syndrome/​Secondary HLH (MAS/​sHLH). National Library of Medicine. ClinicalTrials.gov Identifier: NCT03311854. Last Updated May 17, 2022. Accessed June 30, 2025. https://www.clinicaltrials.gov/study/NCT03311854

3. Evaluate Efficacy, Safety and Tolerability, PK and PD of Emapalumab in Children and Adults With MAS in Still's or SLE (EMERALD). National Library of Medicine. ClinicalTrials.gov Identifier: NCT05001737. Last Updated June 11, 2025. Accessed June 30, 2025. https://clinicaltrials.gov/study/NCT05001737?tab=table

4. McGovern G. Emapalumab-lzsg receives FDA priority review for treatment of children and adults with HLH/MAS. Pharmacy Times. Published March 4, 2025. Accessed June 30, 2025. https://www.pharmacytimes.com/view/emapalumab-lzsg-receives-fda-priority-review-for-treatment-of-children-and-adults-with-hlh-mas