Biogen Idec
A pedestrian passes the sign outside the headquarters of Biogen Idec Inc. in Cambridge, Massachusetts Reuters

Shares in US drugmaker Biogen Idec surged to new highs after the company announced positive results from the trials of its Alzheimer's drug, boosting its market capitalisation by several billions of dollars.

The company is now valued at almost $112bn (£75.6bn, €104.4bn), after its shares closed up 9.76% at $475.98 on 20 March. Including the $40bn surge on a single day, the company's market cap rose fivefold over the last five years.

Biogen released initial results of the study in December, and its shares have surged 54% since then.

On 20 March, the company released positive interim results from its phase 1B study of investigational Alzheimer's treatment aducanumab.

The company said: "Aducanumab demonstrated an acceptable safety profile and positive results on radiologic and clinical measurements in patients with prodromal or mild Alzheimer's disease (AD)."

Aducanumab produced a dose- and time-dependent reduction of amyloid plaque in the brain in the trial treatment of 166 patients. Higher doses and longer treatment durations yielded bigger improvements.

"This is the first time an investigational drug for Alzheimer's disease has demonstrated a statistically significant reduction on amyloid plaque as well as a statistically significant slowing of clinical impairment in patients with prodromal or mild disease," said Alfred Sandrock, MD, PhD, group senior vice president and chief medical officer at Biogen Idec.

"Based on these results, we are advancing the aducanumab clinical programme to phase 3 with plans to initiate enrolment later this year."

Positive results from phase 3 trials that involve a large number of patients would lead to the approval of the drug, which is expected to generate billions of dollars of sales per year for the company.