Collegium Pharmaceutical Inc. said it plans to acquire all outstanding shares of Biodelivery Sciences International Inc. for $5.60 each, putting the price tag at about $604 million. At the heart of the deal are Biodelivery Sciences' Belbuca (buprenorphine buccal film), a schedule III opioid, and Elyxyb (celecoxib), an oral migraine treatment that gives Collegium a foothold into the neurology market.