Elan (ELN) was granted FDA approval of Tysabri for Multiple Sclerosis in November 2004. It was great news for the firm and its shareholders, as it was no secret that the drug was a breakthrough expected to become bestseller in a huge market. The celebration of the great achievement was of short duration. Three patients developed PML (progressive multifocal leukoencephalopathy), two of them died. It was Biogen Idec, Elan’s partner on Tysabri, not the FDA, which decided to withdraw the drug from the market. The FDA was aware that the reward from such a great drug outweighs the risk, which is a rare complication that would occur with any drug that compromises the immune system and there are many on the market. Bottom line, Tysabri was reinstated on the market on condition that the patients take part in a risk-minimization program with mandatory patient registration and regular follow-up. More...