Actavis has entered into a definitive agreement to acquire Allergan in a transaction valued at approximately $66 billion, creating a top 10 global pharmaceutical company with combined annual pro forma revenues of more than $23 billion anticipated in 2015. The transaction was approved by the boards of directors of both companies.    Brent Saunders, chief executive officer and president of Actavis will lead the combined company and Paul Bisaro will remain executive chairman of the board. The senio...