On September 24, 2025, Biogen announced that the U.S. Food and Drug Administration issued a Complete Response Letter (CRL) for the supplemental New Drug Application (sNDA) for the high‑dose regimen of nusinersen (Spinraza) for spinal muscular atrophy (SMA). The CRL requested an update to the Chemistry, Manufacturing and Controls (CMC) module of the application and did not cite deficiencies in the clinical data.
The high‑dose regimen had recently been approved in Japan and is under review by the European Medicines Agency and other global regulators. The CRL represents a regulatory setback that could delay the availability of the expanded dosing option in the United States, potentially impacting Biogen’s revenue growth from its flagship SMA therapy.
Biogen indicated it will resubmit the application promptly using readily available information. The company remains committed to bringing the high‑dose regimen to patients, but the CRL underscores the need for additional technical data to satisfy FDA requirements.
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