Several experts are wondering how best to determine which spinal muscular atrophy (SMA) patients will benefit most from treatment with Spinraza (nusinersen), due both to its high cost and growing demand.

Dr. Claudia A. Chiriboga, a neurology and pediatrics professor at Columbia University Medical Center, said Spinraza must be given every four months at high doses, a regimen that increases demand and creates a managing problem for clinicians.

“There are many children and adults waiting for treatment,” Chiriboga said in an article by Thomas R. Collins that appeared in Neurology Today. “So, how to fairly and equitably prioritize treatment across the patient population is a challenge and also how to assess risk-benefit, for maybe children who are too weak and (for whom) the procedure might be a problem if they need intubation.”

In December, the U.S. Food and Drug Administration (FDA) approved Biogen‘s Spinraza, making it not only the first FDA-approved therapy for SMA, but also one of the most expensive drugs ever approved by the agency.

The drug’s per-dose price tag is $125,000. It helps infants with SMA survive longer and achieve motor milestones.

“Given the extreme [high] cost of the medication and our finite resources, how do we best determine who will benefit from the medication as function that can be recovered, and how do we assess response to medication that justifies continued use?” Chiriboga asked.

“We’re still grappling with these issues,” she said. “We’ve identified the central functions such as walking or sitting and critical functions such as operating their wheelchair that we’d need to preserve. But we don’t have all the answers, and some insurance plans are taking it upon themselves to make those determinations for us, with some criteria that don’t make all that much sense.”

Dr. Charlotte J. Sumner, an associate professor of neurology at Johns Hopkins University, said final results for the Phase 3 ENDEAR clinical trial (NCT02193074) emphasize the need for early treatment of this disease.

“The early and efficient diagnosis of SMA is really critical to attaining the maximal therapeutic benefit from nusinersen or other drugs that are coming in the pipeline. Particularly for infantile SMA, time is motor function,” Sumner said, adding that if neonatal screening for SMA becomes the norm, “we’re going to have to develop infrastructures to be able to efficiently enroll patients in treatment.”

While these results are promising and show that infants can tolerate the spinal injections, the procedure is still challenging. Therefore, “these infants are still very ill and require excellent standard of care,” she said.

It’s still not clear if Spinraza remains effective over time, Sumner said, even though babies who have received the drug for the past four years show that Spinraza hasn’t lost its effectiveness.

“A big question, of course, given the burden of administering this drug, is whether at some point the drug can be withdrawn later in life,” she said. “We do think of SMA somewhat as a disease of development. And perhaps after the developmental period has completed, we can actually withdraw the drug.”