Heart-breaking anecdotes from the patients, parents and doctors of children with the ultra-rare and fatal Barth syndrome won over an FDA advisory committee on Thursday, likely setting up a tough decision for regulators in the coming months.
The FDA’s Cardiovascular and Renal Drugs Advisory Committee voted 10-6 that Stealth BioTherapeutics’ drug elamipretide was effective at treating the disease.
The surprising vote followed questions raised by the committee about drawing conclusions from the use of a natural history data-based trial, as well as the variability of the effects seen in a small placebo-controlled trial. While some committee members saw data from a walk test as a positive signal from the drug’s pivotal trial, others questioned the reliability of the data.
“We very clearly heard there are dismal outcomes without the drug and just the hope may have been the reason for some of these individuals,” panelist Carole Tucker of the University of Texas Medical Branch said after her positive vote, noting she looks forward to seeing more postmarket data.
The FDA has until Jan. 29, 2025, to make a final approval decision.
Only about 130 boys and young men in the US have the mitochondrial disease, which currently has no approved treatments or any others nearing approval. Barth syndrome is characterized by skeletal muscle weakness, delayed growth, fatigue and heart muscle weakness.
The FDA’s reviewers raised many questions about whether the drug, which was previously rejected, can be considered effective. And they also asked whether the 24-patient trial was even enough to be considered a well-controlled trial sufficient for for approval. The company, meanwhile, pointed to the safety of its drug and the totality of the data from the placebo-controlled trial, as well as anecdotal results from an open-label extension.
Only 12 patients received the drug in the placebo-controlled, double-blind trial. The FDA’s reviewers told the committee that Stealth’s data didn’t show a statistically significant difference between elamipretide and placebo on its primary or secondary endpoints.
Ten of the 12 patients in the initial trial went on into an open-label extension study, where the company said they continued to do well. But the FDA reviewers noted that just eight boys remained on treatment after 3.2 years, and only three boys stayed on the drug until 3.7 years.
Patients, parents and doctors of infants, toddlers and children with Barth syndrome called for the drug to be approved during the open public hearing, saying it did help with gaining weight and doing activities that weren’t possible prior to treatment. The panelists went back and forth with FDA’s Office of New Drugs Director Peter Stein on postmarketing and labeling questions, as well as questions on whether the data could amount to enough for an approval.
Even after the “incredibly compelling anecdotal information,” as one unidentified committee member put it, others questioned the fundamentals of the elamipretide trial.