Shares of Tanox ( TNOX) surged nearly 45% after Genentech ( DNA) set plans to buy the company for $20 a share. The deal is worth about $919 million. Tanox was up $6.11 to $19.75.

Siga Technologies ( SIGA - Get Report), a developer of antiviral medications, said it has received contracts from the Air Force worth $2.3 million, lifting its shares 2.5%. Siga was up 10 cents to $4.06.

Mylan ( MYL - Get Report) got Food and Drug Administration approval to sell a generic version of Alza's Ditropan extended-release tablets for treating bladder ailments. Pittsburgh-based Mylan said it will launch its Oxybutynin Chloride tablets immediately. Shares were up 3.1% to $20.64. Shire ( SHPGY) sued Watson Pharmaceuticals' ( WPI) Andrx unit, claiming patent infringement on Shire's Adderall attention deficit disorder drug. The news comes just a day after Corona, Calif.-based Watson completed its acquisition of Andrx. Watson rose 1.1% to $24.84, and Shire was up 0.7% to $56.52.

A panel of medical experts is recommending that U.S. regulators approve a new use for Medtronic's ( MDT - Get Report) Infuse bone graft by expanding its indications to oral and maxillofacial procedures. Still, Medtronic edged down 6 cents to $48.96.