The Food and Drug Administration on Monday approved Biogen's Alzheimer's treatment, ushering in the first new drug for the disease in nearly two decades.

The drug, which was previously known as aducanumab but will be sold under the brand name Aduhelm, is designed to erode the sticky plaque that builds up in the brains of people with Alzheimer's. Scientists have theorized that the substance kills brain cells and causes the memory loss that characterizes the disease.

In clinical trials, Aduhelm reduced the levels of those plaques but wasn't definitively shown to improve memory and cognition. The FDA approved the drug under a special accelerated pathway that allows for the use of drugs that are reasonably likely to have a benefit for patients even when there is uncertainty about how well they work.

An FDA advisory committee said in November that Biogen's tests had failed to show that the drug effectively treated Alzheimer's. The FDA generally follows the advice of its advisory committees.

"There has been considerable public debate on whether Aduhelm should be approved. As is often the case when it comes to interpreting scientific data, the expert community has offered differing perspectives," Dr. Patrizia Cavazzoni, the director of the FDA's Center for Drug Evaluation and Research, said in a statement on Monday.

"The Agency concluded that the benefits of Aduhelm for patients with Alzheimer's disease outweighed the risks of the therapy."

Close to 6 million Americans have Alzheimer's, meaning the market for the drug could be substantial.

Biogen hasn't said how much it will charge for the treatment. Citi and SVB Leerink analysts have estimated that Aduhelm could drive US$10 billion to US$12 billion in annual revenue. Biogen has invested more than US$2 billion in developing aducanumab and other experimental Alzheimer's drugs.

Biogen's stock surged 58 percent to US$450.62 after the approval decision, giving the company a market value of about US$69 billion.

Though the clinical trial found that Aduhelm worked on a subset of participants, the FDA will allow for widespread use of the treatment. Patients will need brain scans to monitor for small hemorrhages known as amyloid-related imaging abnormalities, or ARIA.

Neither Biogen nor the FDA immediately disclosed when it would become available.

Aducanumab's rocky road to the FDA almost ended in failure 2 years ago

Biogen's FDA application hinged on two identical late-stage clinical trials that were shut down in early 2019 after an interim analysis indicated they would likely fail.

But Biogen didn't cut its losses; the company continued to parse the data. Roughly six months later, Biogen surprised the drug industry by announcing that a subset of participants in one of the trials had been showing positive signs. The participants' amyloid plaque levels were down, and their ability to recall words, remember life events, prepare meals, and complete other everyday tasks had improved, the company said.

Those test results were the bedrock of Biogen's FDA application, but data from the other failed late-stage trial and another early-stage trial were also included. The separate outcomes of the late-stage, or phase-three, tests were a point of contention during the FDA's review of the drug.

David Knopman, a neurologist who was involved in Biogen's clinical trials, last year called on the biotech firm to run a new late-stage trial, saying the data Biogen had presented didn't prove that the drug helped patients.

"Perfection may be the enemy of the good, but for aducanumab, the evidence doesn't even rise to 'good,'" he wrote to the FDA in October.

"Contrary to the hope that aducanumab will help Alzheimer patients, the evidence shows it will offer improvement to none, it will harm some of those exposed, and it will consume enormous resources."

The advisory committee, which included researchers, clinicians, and a biostatistician, largely said that Biogen's argument in favor of approval was full of holes. But FDA officials said they found the data from the successful phase-three trial "robust and exceptionally persuasive" and determined that the positive trial results could back up Biogen's application.

Biogen spent $2 billion developing its Alzheimer's drugs over the past 5 years

Brian Abrahams, an RBC Capital Markets analyst, estimated in January that Biogen had a 15 percent chance of FDA approval. Others placed Biogen's odds closer to 40 or 60 percent, citing cases in which the FDA had approved products for previously untreatable diseases.

Those odds looked even better after the FDA delayed its decision deadline to June 7 from March 7. Deadline extensions commonly lead to an approval, analysts said in January.

Patient-advocacy groups also supported approval, citing the lack of options for patients. The last entirely new drug for Alzheimer's, Namenda, was approved in 2003 for people with moderate to severe forms of the disease. The other drugs to hit the market since have been combinations of new and existing products.

The Alzheimer's field has been filled with trial failures, leading several large pharmaceutical companies to end their work in the area.

Biogen has spent at least US$2 billion developing three potential treatments over the past five years, according to financial statements. One of those drugs was shelved in 2019 because of poor trial results, while another, BAN2401, is still being tested by a partner, Eisai.

Biogen's strategy of targeting the sticky amyloid plaque has been abraded by drug failure after drug failure from other companies. The theory got some support in January when Eli Lilly reported success with an amyloid-targeting drug in a phase-two study.

But most drug companies still working in Alzheimer's treatments have left the amyloid argument behind, instead targeting other neurological elements in the hopes of treating the disease.

This article was originally published by Business Insider.

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