Biogen said an evaluation of its closely watched treatment for amyotrophic later sclerosis by the Food and Drug Administration could take as many as three months longer than previously expected.
Biogen officially submitted its treatment for the disease, called tofersen, for approval earlier this year. By late July, the FDA had agreed to review the drug and issue a verdict no later than Jan. 25, 2023. However, that deadline has now been extended to April 25 to allow regulators more time to comb over new details, the company said.
According to Biogen, the FDA, in conducting its review, requested additional information. The responses the company gave were considered a “major amendment” to its original approval application, which caused regulators to delay their decision.
“We are committed to providing any details the agency needs to complete the review of tofersen,” Priya Singhal, Biogen’s head of global safety and regulatory sciences and interim head of research and development, said in the statement. She added that the company will maintain its early access program for tofersen as the FDA continues assessing the drug.
Tofersen is designed to block the production of proteins created by SOD1, a gene that, when mutated, gives rise to ALS. However, in a key clinical trial the drug wasn’t any better than a placebo at slowing disease progression.
Though the study failed, Biogen said there were still positive signs. For example, patients treated with tofersen experienced significant reductions in a different protein, “neurofilament light chain,” that can be a signal of neurological damage. Biogen ultimately based its application, which was submitted under the accelerated approval pathway, on tofersen’s apparent effect on this protein.
When Biogen disclosed in July that tofersen was under review, the company also said the FDA was planning to convene a panel of outside advisors to weigh in on its application.
The FDA recently took the unusual step of bringing together that same panel twice for another ALS drug known as AMX0035. That drug has since been approved and is sold by Amylyx Pharmaceuticals under the brand name Relyvrio. As with tofersen, the FDA took extra time to evaluate AMX0035.
To some industry observers, such delays aren’t necessarily bad omens. Analysts at Evercore ISI analyzed 156 drug approval applications for which the FDA convened an advisory committee and found that in the 23 cases where the agency extended its review deadline, 18 ended in approval.