Dr. Vasant Narasimhan, CEO of Novartis, speaking at the Healthy Returns conference in New York City on May 21, 2019.

The Food and Drug Administration on Friday approved Novartis' $2.1 million gene therapy for spinal muscular atrophy — making it the world's most expensive drug.

The therapy, Zolgensma, is a one-time treatment for spinal muscular atrophy, a muscle-wasting disease and leading genetic cause of infant mortality that affects one in every 11,000 births. Novartis had previously said it could price the treatment between $1.5 million to $5 million.

Novartis said the treatment will cost $2.1 million — or $425,000 a year spread out over five years. The company said it's "working closely with insurers to create 5-year agreements based on success of the treatment as well as other novel pay-over-time options." It's currently in "advanced discussions" with more than 15 insurers on payment options. Shares of Novartis were up nearly 4% late-afternoon Friday.

This marks a new era in medicine where new therapies can cure patients in a single treatment — but at a high price. Insurers and governments will need to figure out how to pay for these therapies and society will need to decide whether any drug, even lifesaving ones, are worth millions of dollars.

"Zolgensma is a historic advance for the treatment of SMA and a landmark one-time gene therapy," Novartis CEO Vas Narasimhan said a statement Friday. "Our goal is to ensure broad patient access to this transformational medicine and to share value with the healthcare system."