With the last major uncertainty for Tecfidera dimethyl fumarate in the rearview mirror, Royalty Pharma felt comfortable buying a bigger chunk of the MS drug's royalty stream. The firm is shelling out $510 million in cash for a larger stake, and now has bet more than $1 billion on the drug's prospects.

Royalty is buying the stake from former shareholders of Fumapharm AG, who are eligible for sales milestones related to Tecfidera (BG-12) and psoriasis drug