Royalty Pharma has acquired an additional interest in Biogen Idec's multiple sclerosis pill Tecfidera for $510 million in cash.

Royalty, which last year tried to acquire Ireland's Elan Corp, has bought the earn-out payable to former shareholders of Germany's Fumapharm, which was bought by Biogen in 2006. The earn-out primarily represents indirect interests in the sales of Tecfidera (dimethyl fumarate), which was launched last year and has already become a major seller, and a psoriasis treatment Fumaderm (fumaric acid).

This acquisition follows Royalty's previous acquisition of an interest in the Fumapharm earn-out payments in May 2012 for $761 million. The company already has certain rights to several big-selling drugs, including AbbVie's Humira (adalimumab) and J&J/Merck & Co's Remicade (infliximab), and most recently spent $485 million to acquire Quest Pharmaceutical’s royalties on Johnson & Johnson/Pharmacyclics lymphoma drug Imbruvica (ibrutinib).