A DRUG which could slow the progression of Alzheimer’s disease has been approved by regulators in the US, in a landmark moment for patients worldwide.

The US Food and Drug Administration (FDA) said there was “substantial evidence that aducanumab reduces amyloid beta plaques in the brain” and that this “is reasonably likely to predict important benefits to patients”.

It is the first time in almost 20 years that a new medication for the condition has been approved, and the first drug to target the underlying disease process rather than the symptoms.

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Thousands of patients in Scotland who are in the earlier stages of the disease, with mild cognitive impairment, could be eligible for the treatment although it is unlikely to become available on the NHS until 2022 - subject to meeting with UK regulators’ approval.

Professor Craig Ritchie, director of Brain Health Scotland and a leading expert in the psychiatry of ageing and Alzheimer’s disease at Edinburgh University, said the FDA announcement was “broadly anticipated” but “opens a new chapter” for patients.

He added: “Use within the NHS though remains some months away and it is critically important that the safe use of this intervention in those people most likely to benefit is fully considered.

“We also need to ensure that we collect real world data on the benefits and side effects of the medication to help us to refine how to use this intervention well. It’s certainly a new chapter but by no means the end of the story.”

Aducanumab, which is administered to patients in the form of a monthly infusion, targets the amyloid protein clumps which accumulate in the brains of people with Alzheimer’s, leading to deterioration in functions such as language, memory, and thinking.

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The drug had faced controversy after a late-stage clinical trial involving around 3000 patients was suspended in March 2019, amid evidence that the drug was no better than a placebo at slowing the progression of Alzheimer's.

However, a subsequent analysis of additional data by US manufacturer Biogen concluded that the drug did work, as long as it was given in higher doses. The company also said it significantly slowed cognitive decline.

Aldo Ceresa is among the participants on the international clinical trial.

The 68-year-old former surgeon, who is originally from Glasgow and now lives in Oxfordshire, took aducanumab for two years before the trial was halted, but is back on the drug as part of a London-based clinical trial.

Mr Ceresa says he has noticed improvements including being "not quite as confused".

He said: "Before, if I was going to get something, I couldn't remember, you know, where to find things in the kitchen.

"That has become less of a problem."

A cure for dementia remains one of the holy grails in medicine with more than 100 potential Alzheimer's drugs failing in the past decade alone, and continued scepticism from some who insist that the evidence that aducanumab works is still too weak.

Robert Howard, a professor of old age psychiatry at University College London, said described the drug's approval as a "grave error that will have only negative impact on patients and their families and that could derail the ongoing search for meaningful dementia treatments".