Eisai Co. and Biogen Inc.’s Alzheimer’s drug Leqembi has been granted full approval by the Food and Drug Administration, making it the first disease-slowing drug to secure that full blessing.

In theory, the move should significantly expand Leqembi’s availability to patients eagerly awaiting new and better options to alter the course of that mind-robbing disease. In practice, the rollout is likely to take longer than patients and their families would like.

Peter Ljubenkov, a neurologist at the UCSF Weill Institute for Neurosciences, is excited to finally be able to offer his patients Leqembi, but stresses that “this drug requires a lot of expertise to give and a lot of infrastructure to give.” He has been part of the months-long effort to prepare the University of California hospital network for Leqembi’s arrival, a work in progress at memory centers around the country.

Leqembi received a conditional approval from the FDA in January. But its use was severely limited because the Centers for Medicare & Medicaid Services said it would not pay for the drug, which carries an annual list price of $26,500, until it had received full approval based on evidence that it could slow down the course of the disease.

With last week’s announcement, Leqembi has cleared that hurdle. But many pieces still have to fall into place before most patients will be able to receive it, says Amanda Smith, director of clinical research at the University of South Florida’s Health Byrd Alzheimer’s Institute.

The first challenge is identifying the right patients. To be eligible, people need to be in the early stages of the disease and have confirmation they have Alzheimer’s and not another form of dementia. That requires objective evidence that their brains are coated with clumps of protein called amyloid, which the drug clears away. That requires either a special PET scan that detects amyloid or a lumbar puncture to analyze cerebral spinal fluid.

But there’s a catch: Amyloid PET scans, the less invasive detection method, are not covered by Medicare. The health agency’s longstanding argument against coverage has been that the test, which can cost $3,000 or more, isn’t necessary for treatment. Leqembi’s approval undermines that argument. CMS should promptly agree to pay for these scans.

And there’s another hurdle. Even if a patient’s disease is confirmed by tests, neurologists will need to have a nuanced discussion with the patient about the risks of Leqembi. People taking blood thinners, for example, or those with two copies of a gene called ApoE4, are are at a higher risk of experiencing more serious brain bleeding and swelling – a side effect the FDA underscored by adding a black box warning to the drug’s label.

Even without those risk factors, patients will need an MRI to confirm they don’t have signs of brain bleeding before treatment begins, and then several more scans during treatment to monitor for swelling or bleeds.

Finally, there’s one more obstacle: Medicare’s requirements for coverage of the drug. CMS will only pay for Leqembi (and any similar drugs that receive approval) if data is collected on the drug’s efficacy and safety in the real world, rather than in the highly regimented setting of a clinical trial. To capture that information, physicians will have to register patients in a yet-to-be determined registry. Without knowing how onerous that registry will be, it is “probably the next rate-limiting step toward getting people this drug in an equitable way,” Ljubenkov says.

All of this could be even more difficult to manage if lots of patients wants the drug. “In theory, as soon as that FDA approval comes out, we may see an influx of patients that are unlike the typical patients that go to memory clinics,” Ljubenkov says. Usually, people come to a clinic late in their disease, but now that there’s a treatment available for mild disease, patients just starting to experience symptoms may be more motivated to get a diagnosis, he says.

Access isn’t the only challenge facing the drug. Some physicians might prescribe it too readily. “My biggest fear is that the community doctors might just prescribe it without really understanding the implications of it – and prescribe it for people who it is really not appropriate for,” Smith says. She’s already seen how this can go when she inherited patients from a physician who had overprescribed Aduhelm, an earlier Alzheimer’s drug whose conditional approval severely limited its use. “Fully half of them were people I never would have started on it in the first place because they were already too advanced,” she says.

But the FDA’s decision is an important first step. Leqembi’s approval puts us on the path to figuring out a better system for caring for patients as the next drugs come along. Let’s hope it’s just a bumpy beginning to a new era in Alzheimer’s treatment.