As pharma watchers know, aducanumab's fate at the FDA will be pivotal for Biogen, which is facing competitive pressures for its other blockbuster medicines, like Spinraza, the company's spinal muscular atrophy drug, and its multiple sclerosis drug Tecfidera. RELATED: Biogen's sales slide on Spinraza, Tecfidera as pivotal Alzheimer's decision nears First-quarter U.S. sales of Spinraza plunged nearly 37% compared with the same period last year to roughly $149 million. Spinraza has faced growing competition from alternative treatments in the U.S, including Roche's oral option Evrysdi and Novartis's gene therapy Zolgensma.