Perrigo has agreed to sell rights to the royalty stream from sales of the multiple sclerosis drug Tysabri. Royalty Pharma will pay $2.2 billion in cash up front to Perrigo and up to $650 million more in possible milestone payments to get royalties from Jan. 1 onward. Tysabri is sold by Biogen, which had nearly $2 billion in 2016 sales of the drug. Perrigo acquired royalty rights in 2013 when it bought Elan, which had partnered with Biogen to develop the drug. Royalty Pharma owns interests in more than 40 approved drugs and has invested over $850 million in R&D funding in exchange for future royalties on products still in development.