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For 69-year-old Bill McKay, the FDA’s approval this week of Biogen's controversial Alzheimer’s drug offers hope that the veteran of 29 marathons can keep on running.

“Let's work on just being healthy and trying to extend my life as far as it will go.”

His wife Jill is hopeful the treatment will prevent her husband, who is in the early stages of the disease, from getting lost along the way.

“That's a big worry for me. I work full time and so I'm not home during the day, and he goes out for a run. I wonder, am I going to get that phone call? ‘Bill should have been back 45 minutes ago, and we don't know where he went.’"

Bill McKay already qualifies for Biogen's drug, called Aduhelm - the first new treatment for Alzheimer's in nearly two decades and the first to target a cause of Alzheimer’s by removing amyloid plaques from the brain.

But the drug’s approval comes with major asterisks: in two large clinical trials, Aduhelm showed a benefit in one but not the other, and a panel of outside experts said the data failed to prove that the medicine works.

And some trial patients experienced potentially dangerous brain swelling.

It’s why his doctor, Michigan neurologist Cara Leahy, is adamant about cautioning patients not to look to Aduhelm as the holy grail.

"So, there is going to be a lot of important education that we discuss with patients with a realistic idea of what this medication is and what it is not, so to make sure that patients understand this is not a cure, that we are hoping that it has some ability to slow down the progression for patients, but that the learning about this medication is ongoing.”

The FDA has required a post-approval trial to demonstrate that Aduhelm does in fact slow cognitive and functional decline, but that could take years.

Its price tag? Roughly $56,000 per year - although it’s not yet clear yet how much the drug will cost patients like Bill McKay, most of whom will be covered by Medicare.

Despite questions about the drug’s effectiveness and cost, the McKays have gone ahead and scheduled an appointment with Dr. Leahy for next week.

[BILL MCKAY]: “I certainly want to be active and certainly be part of my family life - and be a plus to the general population in this area and anywhere else I could be of service to.”

More than 900 medical centers will start intravenous infusions of the drug in as soon as two weeks.