Merck & Co said on Thursday Kenneth Frazier will step down as chief executive officer at the end of June and will be replaced by Chief Financial Officer Robert Davis.

Frazier took the helm in 2011, and the company's stock price has doubled since then. Under Frazier watch, Keytruda has raked in blockbuster sales, becoming one of the leading products in a new generation of oncology treatments.

The company reported a fourth-quarter loss of $2.09 billion, or 83 cents per share, compared with a profit of $2.36 billion or 92 cents per share, a year earlier.

Frazier, 66, was set to retire in 2019, but the company scrapped a policy requiring CEOs to retire at the age of 65.

Frazier will continue to serve on Merck's board as executive chairman for a transition period to be determined by the board, the company said.