United States approves first Alzheimer's drug in 18 years, Biogen's aducanumab

United States health officials have approved the first new drug for Alzheimer's disease in nearly 20 years, disregarding warnings from independent advisers that the much-debated treatment has not been shown to help slow the brain-destroying disease.

The Food and Drug Administration (FDA) said it approved the drug from American biotechnology company Biogen based on results that seemed "reasonably likely" to benefit Alzheimer's patients.

The medication, aducanumab, will be marketed as Aduhelm and is to be given as an infusion every four weeks.

It's the only therapy that US regulators have said can likely treat the underlying disease, rather than manage symptoms like anxiety and insomnia.

The Therapeutic Goods Administration (TGA) is currently evaluating aducanumab for the treatment of Alzheimer's disease in Australia.

Biogen Australia New Zealand said an outcome of the TGA's review was expected to be made available next year.

"After decades of investment into the research and development of treatments for Alzheimer's disease and over 100 clinical trial failures, there is finally a medicine that addresses a defining pathology of the disease, by reducing amyloid beta plaques in the brain, that we hope will transform the treatment of many people living with Alzheimer's disease," Biogen Australia New Zealand said in a statement.

The FDA's decision, which could impact millions of Americans and their families, is certain to spark disagreements among physicians, medical researchers and patient groups.

It also has far-reaching implications for the standards used to evaluate experimental therapies, including those that show only incremental benefits.

The new drug, which Biogen developed with Japan's Eisai Co, did not reverse mental decline, only slowing it in one study.

Under terms of the so-called accelerated approval, the FDA is requiring the drugmaker to conduct a follow-up study to confirm benefits for patients. If the study fails to show effectiveness, the FDA could pull the drug from the market, though the agency rarely does so.

Biogen said the drug would cost approximately $US56,000 ($72,000) for a typical year's worth of treatment, and said the price would not be raised for four years. Most patients won't pay anywhere near that amount thanks to insurance coverage and other discounts.

The company said it aims to complete its follow-up trial of the drug by 2030.

Caleb Alexander, an FDA adviser who recommended against the drug's approval, said he was "surprised and disappointed" by the decision.