Change of control calculus

The fate of Biogen Idec Inc.'s two partnered drugs - Tysabri natalizumab and Rituxan rituximab - took center stage last week following BIIB's announcement the prior week that it is considering being acquired and has received interest from several parties, including financier Carl Icahn.

BIIB (Cambridge, Mass.) opened on Monday at $83.35, up $13.92 (20%) from the previous Friday, then cooled to close the week off $3.13 to $80.22...