Another win for gene therapy with the approval of Novartis AG's spinal muscular atrophy treatment Zolgensma will likely pose a threat to the disease's only other approved treatment, Biogen Inc.'s Spinraza, but carries a hefty price tag.

The U.S. Food and Drug Administration cleared the drug a week ahead of its expected decision date. Zolgensma, engineered by Novartis' gene therapy unit AveXis Inc., is approved as an intravenous treatment for spinal muscular atrophy, or SMA, in patients less than two years of age. This indication includes all types — types 1, 2 and 3 SMA — as well as presymptomatic disease.

Novartis also announced the price point for Zolgensma, a topic of much debate and discussion in the months leading up to FDA approval. Zolgensma will cost $2.1 million total, or $425,000 a year for five years.

Though U.S. pricing watchdog Institute for Clinical and Economic Review determined in its final report for Spinraza and Zolgensma that both medicines are too expensive, ICER had said in December that Zolgensma would be more cost-effective.

According to AveXis president Dave Lennon, Zolgensma's price is "projected to be 50% below the ultra-rare cost-effectiveness threshold in health economic analysis that has been done to date."

During Novartis' and AveXis' conference call following Zolgensma's approval, Lennon pointed out that Spinraza's cost over 10 years adds up to over $4 million.

Novartis CEO Vasant Narasimhan also said the Swiss drugmaker is advocating for pay-over-time or outcomes-based payments as novel models, having already reached out to the federal government.

Evercore analyst Umer Raffat added, "It's very clear that Novartis has spent extensive time in payer outreach well ahead of this launch — and even issued a separate press release going through payer progress."

Novartis has already partnered with specialty pharmacy Accredo for a payment option allowing for five-year outcomes-based agreements. Jefferies analyst Peter Welford wrote May 24 that AveXis is also in "advanced discussions" with more than 15 payers.

Efficacy and administration, compared with Spinraza

Despite Zolgensma's steep price tag, analysts at the American Academy of Neurology meeting earlier in May said the gene therapy would likely be more appealing to patients currently on Spinraza, which requires a regular spinal injection that, according to Leerink analysts, results in a "heavy Spinraza treatment burden" for both patients and physicians.

"The treatment burden on neurologists from Spinraza is likely to color physician views of Zolgensma and [Roche Holding AG's experimental SMA drug] risdiplam, as treating patients with these agents in place of Spinraza would provide relief from the intrathecal injection burden currently impacting SMA treating physicians' practice hours and resources," Leerink analysts said May 8.

Further pulling patients away from Biogen's RNA-based treatment Spinraza — which is currently a major contributor to the Cambridge, Mass.-based company's revenue — is the unlikelihood of a need for combination therapy, according to Novartis and Leerink's key opinion leaders, or KOLs, who are neurologists.

During Novartis' call, executives said though they would offer rebates for patients who do not see the drug's promised effects over five years, Spinraza should not be needed as maintenance therapy after Zolgensma is administrated.

Leerink's KOLs also cited "lack of relevant data" and possible reimbursement issues to render combination therapy of Zolgensma and Spinraza unlikely, adding that payers in both Europe and the U.S. would be reluctant to cover such pricey treatments altogether.

However, one European KOL expressed doubt that gene therapy will provide a "truly lifelong treatment benefit, and patients would likely need to be maintained with either Spinraza or risdiplam if gene therapy durability begins to wane."

AveXis' presentation at the American Academy of Neurology meeting revealed that Zolgensma was effective up to four years after treatment.

Zolgensma is also being formulated for spinal injection administration, which Leerink analysts expect will enter the market in 2021.