Merck & Co. (NYSE: MRK) says its board of directors named Kenneth C. Frazier chief executive officer to succeed retiring Richard T. Clark.

Frazier is currently Merck’s president and a member of the board of directors. Clark has been CEO since 2005 and will remain as chairman of the board. His retirement was expected in 2011, and the changes are effective Jan. 1.

“Merck’s Board of Directors and I have great confidence in Ken as the right CEO to lead this exceptional company into a new era of global health care,” Clark said in a statement. “Ken has made considerable contributions to our business every step of the way during his 18 years with Merck. His intellect, drive and deep understanding of our industry will greatly benefit Merck and our mission of improving and saving lives through scientific innovation. Ken is a gifted leader who has what it will take to ensure Merck’s success as we face unprecedented change and enormous opportunity.”

The management change comes a year after Whitehouse Station, N.J.-based Merck bought Schering-Plough Corp. for $41 billion.

Merck is in the process of a $300 million expansion of its vaccine manufacturing facilities in Durham, N.C.

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