CHICAGO, July 30 (Reuters) - The benefit of Eisai ( ESALF )

and Biogen's Alzheimer's drug Leqembi in

patients with early-stage Alzheimer's appears to increase with

continued use with no new safety issues, according to three-year

data presented at an Alzheimer's meeting on Tuesday.

In the companies' pivotal clinical trial, Leqembi reduced

cognitive decline by 27% after 18 months - data that supported

the drug's approval last year.

The new study looked at how the drug performed in about 95%

of trial patients who continued on the treatment. After three

years, Leqembi slowed cognitive decline by 31% compared to what

would be expected in similar patients who did not receive

treatment.

There were no new safety findings over the three-year

period. Brain swelling and bleeding associated with drugs that

work by removing amyloid plaque from the brain largely occurred

within the first six months of treatment, Dr. Christopher van

Dyck, director of the Yale's Alzheimer's Disease Research Unit,

told the meeting.

A separate analysis of data from a midstage study looked at

patients who had a gap in treatment of 9 to 59 months following

18 months of initial treatment. In that study, there was still a

difference, but once treatment stopped, the rate of cognitive

decline reverted back to what was seen in patients on placebo.

Discontinuation of treatment also showed increases in

Alzheimer's-related disease biomarkers, such as the return of

amyloid plaques.

The findings were part of several presentations at the

Alzheimer's Association International Conference in Philadelphia

aimed at showing that Eisai's ( ESALF ) drug continues to benefit patients

who stay on Leqembi after amyloid has been removed.

Eisai's ( ESALF ) drug targets protofibrils - toxic building blocks

that eventually form clumps in the brain known as amyloid

plaques, a hallmark of Alzheimer's disease. Leqembi both removes

amyloid plaques and continues to target protofibrils, which can

injure brain cells.

"There is no question long-term benefit is better than

short-term benefit," Dr. Lynn Kramer, Eisai's ( ESALF ) chief clinical

officer, told Reuters.

The studies underline differences between Eisai ( ESALF ) and Biogen's

treatment and Eli Lilly's ( LLY ) Alzheimer's drug Kisunla

(donanemab), which was approved on July 2.

The Lilly drug exclusively targets amyloid plaques. Once the

brain plaque is gone, patients can discontinue treatment.