After just 2 years on the market (actual detailing did not begin until Jan 2007), Tyasbri's market share is 7.5%. I believe Copaxone has been on the market for approx. 10+ years.
What should be troubling to you (if you’re long BIIB or ELN) is that the drug that’s relatively new (Tysabri) has already flatlined in market share, while the drug that’s been around since the beginning of time (Copaxone) is still gaining share.
p.s. As far as prices are concerned, I think you need to do more digging to ascertain the ASP of each drug on a worldwide basis.
“The efficient-market hypothesis may be the foremost piece of B.S. ever promulgated in any area of human knowledge!”