An expensive new drug that can slow the progression of Alzheimer's disease was approved by Health Canada on Friday.

While existing medications treat Alzheimer's symptoms, lecanemab is the first drug authorized in Canada that targets the disease's underlying cause in order to reduce the rate of cognitive and functional decline.

"This is an important milestone," neurologist Dr. Sharon Cohen told CTVNews.ca. "What this does is slow down the disease at an early stage where people are still living at home and functioning quite well."

Cohen, who was involved in clinical trials of the drug, is the medical director of the Toronto Memory Program, a clinic that specializes in the diagnosis and treatment of Alzheimer's and related disorders.

"If you think about the treatments we've had so far for Alzheimer's disease, they've been directed at the dementia stage of the disease, where people are already dependent," Cohen explained by phone on Monday. "Now we have something that goes much earlier in the disease ... this is a big deal."

According to Cohen, Canadian patients could receive their first doses of lecanemab by the end of 2025. In the U.S., where it has already been approved, the drug costs a staggering US$26,500 per year. Treatment also requires several MRIs to monitor for side effects.

It took more than two years for Health Canada to approve the drug, which was developed by Japanese pharmaceutical company Eisai Ltd. and U.S. biotechnology company Biogen Inc. Sold under the brand name Leqembi, Health Canada granted conditional authorization for the drug on Friday, pending the results of trials to verify its clinical benefits. The drug has already been approved in 51 other countries and regions, including Japan, the U.S., China and the European Union.

"There are 35,000 individuals already on treatment with lecanemab commercially," Cohen said. "So there's a great deal of real-world evidence already from countries where the drug has been approved."

While lecanemab does not cure Alzheimer's, it can slow it down. The drug works by clearing beta-amyloid proteins from the brain. The plaque-like buildup of such proteins has been linked to brain cell death and is one of the telltale signs of Alzheimer's disease. Used for patients with mild cognitive impairment or mild dementia due to Alzheimer's disease, the drug has been shown to delay disease progression by 10 to 13 months.

"If you catch it early and slow it down, people can have a lot more time to do the things that matter to them and to stay independent, including stay in the workforce or travel, make decisions, manage their own finances," Cohen said. "These are things that people with Alzheimer's worry terribly about, that they'll lose their ability to make their own decisions. So, this is huge and we haven't had something like this before."

According to the Alzheimer Society of Canada, an estimated 771,000 Canadians are living with dementia. As Canada's population ages, that number is expected to grow to one million in 2030 and more than 1.7 million by 2050. Alzheimer's disease is the most common form of dementia and accounts for 60 to 80 per cent of all cases. According to the Alzheimer Society of Canada, the time spent by family and friends caring for those with dementia is equivalent to 290,000 full-time jobs. That's expected to climb to 690,000 jobs in 2050.

Dr. Stephen Pasternak is a cognitive neurologist and an associate professor at Western University who specializes in the diagnosis and treatment of neurodegenerative diseases. Pasternak, who was not involved in the development of the drug, describes lecanemab as "a major technical advance" for its proven ability to lower beta-amyloid proteins in the brain.

"Having said that, it is not the slam dunk that we hoped for," Pasternak told CTVNews.ca. "It does not stop people from getting worse, but the disease is slowed. It appears to only be helpful in the mildest patients."

The cost of the drug in Canada has not yet been revealed, but Pasternak expects it will be "substantial."

"Access to neurologists and geriatricians who will diagnose and administer the treatment will be a huge problem in Canada," Pasternak added. "If your geriatrician or neurologist has a one-year waiting list, patients could miss the eligibility window."

While those with private health insurance or the means to pay for the drug will likely be the first to receive it in Canada, Cohen hopes it will eventually by covered by public funding. Either way, she says that by delaying the onset of more severe Alzheimer's symptoms, the drug's price tag will be worth the overall savings it could bring to both individuals and healthcare systems.

"(Alzheimer's) becomes expensive as people become more disabled: so, nursing home placement really escalates the cost to health-care systems, needing in-home help, personal support workers, families having to come out of the workforce to care for a loved one, there are all kinds of personal costs involved," Cohen said. "That is really important for people to understand that this is a cost-saving medication."

Lecanemab is taken by IV every two weeks. Patients are required to have an MRI before starting treatment, as well as four MRIs during the first year to check for serious, but rare side effects, such as brain swelling and microbleeds, which impact less than one per cent of patients.

In addition to costs, MRI availability could pose another barrier to treatment. A recent study commissioned by the Canadian Association of Radiologists highlighted rising MRI wait times, as well as persistent staff and equipment shortages.

"Initially, I was concerned that would be a barrier, but now when I see how receptive radiologists are to this milestone, this breakthrough of new treatment, I think that we'll be OK," Cohen said. "But there will be some geographies in Canada where patients don't have as ready access to MRIs, or will have to travel to a centre with (an) MRI facility available, so it does pose to some extent a barrier, but I think this is doable."

Because of an increased risk of side effects, Health Canada says that lecanemab should not be given to those with two copies of the gene APOE e4 , which is the strongest known genetic risk factor for Alzheimer's. This is something new patients will have to be screened for. Potential patients will also have to be tested for the presence of beta-amyloid proteins to be eligible for treatment.

While countries like the U.S. and Japan began approving lecanemab back in 2023, the Health Canada review took more than double its 300-day target for reviewing drug submissions.

"Let me just say that Health Canada is a little short-staffed," Cohen said. "I'm speculating here, but they certainly don't have the staff required to move an important treatment along quickly. So we're delighted to finally have it, although it's been a long time in coming."

Health Canada did not immediately respond to a request for comment.

Dr. Paolo Vitali is a neurologist, neuropsychologist and an associate professor at McGill University who researches dementia. By slowing the progression of Alzheimer's disease, Vitali says lecanemab will provide a "clinically meaningful benefit for our patients."

"This approval represents a major advancement in the field of Alzheimer's pharmacological treatment," Vitali told CTVNews.ca. "It is the first drug shown to be effective against Alzheimer's disease to be approved in Canada in more than 25 years."