Alzheimer's disease - neurons with amyloid plaques (Photo: Thinkstock)

An experimental Alzheimer’s disease drug from Biogen Inc. and Eisai Co. slowed the progression of the earliest stages of the devastating condition by 30% in a study, a first in the decades-long research that has thus far been littered with failures.

Doctors and patient advocates said the results were encouraging, though more information was needed from larger, longer studies before any real promise from the drug could be accurately measured.

Only the highest of the five doses worked. And while the percentage benefit exceeded analysts’ expectations, the new data was for patients treated for 18 months rather than the 12 months many had anticipated — which muddled comparisons. Investors may have hoped for a fuller success. Biogen fell 10% in late trading Wednesday after closing at the highest in three years ahead of the data presentation.

(Related: Biogen Surges After Positive (But Vague) Report on Alzheimer’s Trial)

The trial itself has been shrouded in secrecy. After an initial analysis using a novel approach failed to find a significant improvement in December, the companies announced three weeks ago that a different approach yielded positive results.

“It’s encouraging, but a lot more needs to be done,” said Julie Schneider, associate director of Rush Alzheimer’s Disease Center in Chicago, and one of the few outside experts who had seen the latest data released Wednesday. “I would not say it’s shock and awe.”

The results for the drug, called BAN2401, were presented at the Alzheimer’s Association International Conference in Chicago. Shares of both Biogen, based in Cambridge, Massachusetts, and Japan’s Eisai had soared earlier this month after the companies presented the initial positive results.

Only the highest dose of the drug showed a significant benefit, slowing the progression of the disease on a novel measure called ADCOMS of 12 items compiled from more traditional approaches. It included performance on word recognition and recall, personal care, memory, problem solving and drawing.

The highest dose of the drug also had a significant benefit on a traditional test of mental function called ADAS-Cog, reducing the cognitive decline by 47% compared with placebo. None of the other doses of the drug were successful.

“It hints at some cognitive effect,” said Maria Carrillo, chief science officer at the Alzheimer’s Association. “We would like to see a larger, more confirmatory trial.

The history of Alzheimer’s research has been marked by a series of high hopes and dramatic setbacks. There have been about 200 failed attempts to find a treatment — so far in vain. The stakes are enormous for the pharmaceutical industry, as well as the millions of people grappling with the disease around the world. A successful drug to slow the progression would be a first in the space, with stratospheric sales and few rivals currently on the horizon.

— Read Spotting Alzheimer’s Early Could Save Americans $7.9 Trillionon ThinkAdvisor.

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