In a rare second review of a new drug application,
By a vote of 7-2, the FDA Peripheral and Central Nervous System Drugs Advisory Committee reversed course on AMX0035 (Amylyx Pharmaceuticals), a combination of sodium phenylbutyrate and taurursodiol.
The panel previously voted 6-4 to reject the drug, ruling that data provided by Amylyx had failed to demonstrate that the survival benefit reported in the only clinical trial of AMX0035 so far was a direct result of the drug.
This time, two panelists who previously voted no were swayed by the drug maker’s new analysis of previously presented research, more than 1,300 public comments in support of the drug, supportive testimony from ALS patients and clinicians, and assurances from company executives that Amylyx would pull the drug from the market if results of an ongoing phase 3 clinical trial show the drug doesn’t work.
“As in March, today we have to have an internal dialogue between our scientific scrutiny and clinical compassion,” said Liana G. Apostolova, MD, from Indiana University, Indianapolis, who originally voted against the application.
“Today I also saw additional confirmatory evidence that was not unequivocally persuasive but was nonetheless reassuring,” Dr. Apostolova said. “Because of that I am voting in support of AMX0035.”
A rare second chance
ALS (Lou Gehrig’s disease) is a progressive, fatal neurodegenerative disease affecting nerve cells in the brain and spinal cord that causes loss of motor control. It is rare, affecting about 30,000 people in the United States with another 5,000 new cases diagnosed each year. Most people with the disease die within 2 years of diagnosis.
The FDA has approved two therapies for ALS, but both have limited efficacy.
Typically, FDA approval requires two large studies or one study with a “very persuasive” effect on survival.
Amylyx’s application is based on a single study, the multicenter, two-phase CENTAUR trial. In that trial, 137 people with ALS received AMX0035 or placebo for 24 weeks.
Researchers found that patients receiving AMX0035 had a 25% slower decline in function, compared with the those taking placebo. A change of 20% or more is considered clinically meaningful.
The investigators also found a statistically significant median difference of 4.8 months in time to death, first hospitalization, or tracheostomy/permanent assisted ventilation in the group originally assigned to receive AMX0035 compared with the group originally assigned to receive placebo (hazard ratio, 0.62; P = .023).
In the panel’s previous vote against the drug application, members cited several issues with the study, concluding that it did not offer persuasive or robust evidence of efficacy. They also cited missing data assumptions in the primary analysis, issues of randomization and imbalances in concomitant use of riluzole and edaravone, the two FDA-approved drugs for ALS.
The FDA later requested additional information from Amylyx, delayed its final ruling on the new drug application to Sept. 29, and called for a second review meeting – a virtually unheard-of move.
An FDA review posted in advance of the meeting Sept. 29 had hinted at a different outcome. In that report, regulators said new data from Amylyx were not “sufficiently independent or persuasive” to establish effectiveness.
However, FDA officials in the meeting stressed the importance of considering unmet medical need in ALS in the panel’s decision-making process.
“Recognizing the substantial unmet medical need in ALS, we feel that it is important that the committee is afforded the opportunity to consider this new information, along with the information presented at the prior meeting, in that context,” Billy Dunn, MD, director of the FDA Office of Neuroscience, said during the meeting.
Panelists heard additional data that Amylyx claims confirms the results of the CENTAUR study, including new analyses of the previously submitted survival data and new data from that study and an open-label extension.
They also provided new information on a biomarker data from a phase 2 study of AMX0035 to treat Alzheimer’s disease.
“I think we note the limitations of the analyses, but we still haven’t taken it off the table that they could be considered as confirmatory evidence and that’s why we’re here today,” said Teresa Buracchio, MD, director of the division of neurology for the FDA.
Two members of the panel who voted no in March stuck with that position at the Sept. 29 meeting.
“Unfortunately, I don’t believe the new evidence we’ve reviewed, while promising, combined with that prior evidence, constitutes substantial evidence of effectiveness,” said panelist Caleb Alexander, MD, a professor of epidemiology and medicine at the Johns Hopkins University Center for Drug Safety and Effectiveness, Baltimore.
Dr. Alexander, who also voted no in March, said that post hoc data presented at the meeting were not enough to assuage concerns that led him and others to reject the drug in March.
A challenging situation
Amylyx is currently leading the 48-week international, phase 3, placebo-controlled PHOENIX clinical trial of AMX0035. The study has enrolled about half of its 600-patient target.
“Undoubtedly, the results of the phase 3 study would be highly informative for a regulatory decision on the current ... review for AMX0035,” said Emily Freilich, MD, of the FDA.
However, results aren’t expected until late 2023 or early 2024, which “places the agency in a challenging situation of potentially making a regulatory decision that may not be subsequently confirmed by the results of the ongoing study.”
In June, Amylyx received conditional approval in Canada for the drug, but final approval depends on the outcome of the PHOENIX trial. The FDA does not offer a conditional approval track.
“If AMX0035 is not approved now, the FDA anticipated decision will likely happen in 2025, underscoring the critical importance of today’s outcome,” said Tammy Sarnelli, MPAHC, global head of Regulatory Affairs for Amylyx Pharmaceuticals.
If the FDA were to approve AMX0035 and results from the PHOENIX trial ultimately fail to prove efficacy, Justin Klee, co-CEO and cofounder of Amylyx Pharmaceuticals, said the company would withdraw the drug.
“To be clear, if PHOENIX is not successful, we will do what is right for patients, which includes voluntarily removing the product from the market,” Mr. Klee said.
Regardless of the company’s decision, FDA officials noted that the agency does have the ability to recall a drug from the market if studies show that it no longer meets requirements for approval.
“The FDA, with all due respect, significantly understates the complexity and likelihood of their pulling a product from the market,” Dr. Alexander said. “Whether or not they can ultimately pull a product from the market is no substitute for the evidentiary thresholds that are required for market access.”
A version of this article first appeared on Medscape.com.