In a late-stage study involving 970 people with primary-progressive multiple sclerosis (PPMS), the Novartis drug Gilenya (fingolimod) failed to show any significant advantages over a placebo in a combination of disability measures the Swiss-based pharmaceutical producer said.

Gilenya is already approved in the US and Europe as a treatment for the more common relapsing-remitting form of multiple sclerosis. It currently is being tested in Phase III trials as a treatment for pediatric MS and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP).

There is currently no approved treatment for PPMS, a form of the disease that involves a steady worsening of brain function and affects about 10% of all people diagnosed with multiple sclerosis worldwide, some 2.3 million.

Gilenya had been predicted to be Novartis's best-selling product by 2016, with analysts forecasting $3.2 billion in sales. "We understand this news is very disappointing for those affected by PPMS," Vasant Narasimhan, head of development at Novartis's pharmaceuticals division, said.

"While PPMS is a focus of the MS community, relatively little is known about the disease, so finding effective treatments remains a challenge," he added.