By John Miller
ZURICH (Reuters) - U.S. regulators have halted a trial of Novartis's (S:NOVN) Zolgensma treatment after an animal study raised safety concerns, the company said on Wednesday, in a setback for the drugmaker's plan to expand its use to older patients.
The U.S. Food and Drug Administration's partial hold on the so-called STRONG trial impacts patients aged up to five with spinal muscular atrophy (SMA) who were to receive a higher dose of the gene therapy via a spinal infusion.
The hold was issued after Novartis told health authorities about the animal study's findings that showed dorsal root ganglia (DRG) mononuclear cell inflammation, a neurological condition sometimes accompanied by nerve damage or loss.
Novartis shares fell 1% at 0715 GMT, while other European drugmakers rose. Analysts said more information was needed to assess whether these findings could have an impact on Zolgensma's long-term prospects.
"We need to better understand, what the issues are and whether there really is a read-through to the human trial," Vontobel analyst Stefan Schneider said.
Novartis said it was working with regulators, in hopes of having the hold released.
Zolgensma, whose $2.1 million list price makes it the world's most-expensive treatment, is already approved for children aged up to two with the deadly muscle wasting disease and is given by infusion into the young patients' veins.
The medicine had $160 million in sales in its first full quarter on the market.
The STRONG study is meant to underpin its expanded approval for older children, where Novartis would also compete with Biogen's (O:BIIB) Spinraza that is already on the market, and Roche's (S:ROG) investigational risdiplam that is due to seek approval this year.
Roche shares were up 0.7%.
"The clinical significance of the DRG inflammation observed in this pre-clinical animal study is not known and was not seen in prior animal studies," Novartis said in a statement.
"We are working with health authorities to confirm further guidance to clinical investigators."
The partial FDA hold halts enrollment of patients getting a higher dose of Zolgensma, also known as AVXS-101, via an spinal infusion, also called intrathecal administration.
Low- and mid-dose portions of the STRONG trial have already been completed, as has presentation of interim results.
"Of note, we have completed a thorough review of human safety data from all available sources to date and no adverse effects related to sensory changes have been seen," Novartis said.