Actavis has completed its $28 billion acquisition of fellow drugmaker Forest Laboratories, and the leader of the acquired company is now the CEO of Actavis.

The Ireland-based drugmaker said Tuesday that Brenton L. Saunders will serve as Actavis president and CEO. Former Actavis Chairman and CEO Paul M. Bisaro, who helped shepherd the company through several multibillion dollar acquisitions, will become executive chairman.

Actavis Plc had announced the cash-and-stock acquisition in February, when it was initially valued at about $25 billion. Actavis said then that Bisaro would lead the combined company.

But three months later, the drugmakers said Bisaro would move to the newly created position of executive chairman, and Saunders would take over as CEO. Actavis said the appointments reflect the complementary expertise of management teams from both companies and the increased size and complexity of the combined business.

Saunders had served as Forest Laboratories Inc. CEO for less than a year. Before that, he led optical products maker Bausch & Lomb Inc., which was acquired by Valeant Pharmaceuticals International Inc.

Actavis also added two Forest Labs board members, Dr. Nesli Basgoz and Christopher J. Coughlin, to its board.

Actavis shares climbed $3 to $226.07 in Tuesday morning trading, while the Standard & Poor’s 500 index rose less than 1 percent.