Biogen slides after disclosing patient additions to studies of Alzheimer's disease drug aducanumab

Shares in Biogen fell as much as 9.1 percent after the company revealed in a presentation to investors that it will add 510 more patients to late-stage studies of the experimental Alzheimer's disease therapy aducanumab. Chief medical officer Al Sandrock explained that the decision was taken as "we did see more variability on the primary endpoint than assumed when we did the original sample size estimations."

According to Biogen, the option to expand the trial was planned, although Robert W. Baird & Co. analyst Brian Skorney said it raises concerns about the results. "Generally, it's not a good sign when the way you designed your study isn't working out appropriately," Skorney commented, adding "aducanumab is considered a very risky pipeline candidate to begin with, just given the history of Alzheimer's trials."

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Biogen spokesman Matt Fearer noted that the company was blinded to whether or not aducanumab is working in the studies, adding that it plans to finish adding the extra patients by midyear. The company licensed the drug, which is thought to target aggregated forms of beta amyloid, from Neurimmune in 2007. Biogen later signed a deal to develop and commercialise aducanumab with Eisai.

The news comes after Merck & Co. earlier in the week said it was ending the Phase III APECS study of verubecestat, formerly known as MK-8931, for the treatment of prodromal Alzheimer's disease following a recommendation by an external Data Monitoring Committee. In its analysis, the committee concluded that the BACE1 inhibitor was unlikely to exhibit a positive benefit/risk ratio if the study continued.

For related analysis, read ViewPoints: Merck & Co. shelves verubecestat – is writing on wall for Biogen, Eli Lilly?

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