The US Food and Drug Administration has refused to approve a higher-dose version of Biogen’s treatment for spinal muscular atrophy (SMA), citing the need for updated technical information in the application. The decision was relayed via a ‘complete response letter’ to Biogen, which clarified there were no issues with the clinical data behind the new high-dose regimen. Biogen says it will resubmit the application promptly, drawing on information that is already at hand.

Spinraza has been on the market since 2016 as a therapy for SMA, a rare genetic condition that causes progressive muscle wasting due to a faulty SMN1 gene. Last year, it generated $1.57 billion in global sales, making it Biogen’s second-highest selling product. The newly proposed high-dose regimen is already available in Japan and is currently being considered by the European Medicines Agency and other regulators.

Under the high-dose proposal, patients would begin with two 50 mg loading doses two weeks apart, then move to 28 mg maintenance doses every four months. This compares to the existing standard 12 mg dose. Clinical trial data submitted by Biogen showed that infants given the higher dose saw significant improvements in motor function compared to untreated patients.

Although the US regulator asked for updates to chemistry and manufacturing documentation, it found no fault with how the drug works or its safety in patients. The new dosage is administered as an injection into the spinal fluid and is designed to further boost the essential protein levels needed for motor neuron health.

The sector is seeing growing competition, with Novartis’s gene therapy Zolgensma and Roche’s oral drug Evrysdi both making headway thanks to their ease of use and broader accessibility. Spinraza remains a major product, but Biogen will be hoping for a rapid review once it resubmits its application, keen to offer the high-dose option to children and families living with SMA in the US.