David Russell, analyst at OptionMonster.Stock and options traders are piling into Biogen Idec ( BIIB) on speculation that the drugmaker could be a takeover target. About 75,000 options contracts traded on the name, more than 10 times the average over the last 20 sessions. About two-thirds of the volume is in calls, according to OptionMonster's tracking systems. Most of the buying is focused on options expiring this month and next. Some 21,500 contracts have changed hands for the April 55 strikes, plus another 13,400 for the April 60 strikes. Both contracts, plus the May 60 calls, traded in volumes that exceeded open interest. Biogen Idec stock rose 6.5% today to $52.85 on volume of about 6.4 million, almost twice the average level. Rumors circulated among European trading desks suggested French pharmaceuticals giant Sanofi-Aventis may offer to buy Biogen for at least $75 a share, according to Reuters.