Kevin Sharer, chairman and CEO of Amgen, is set to retire in May, the Thousand Oaks-based company said on Dec. 15. Current president and chief operating officer Robert Bradway will become the company’s new CEO.

Sharer led Amgen, the largest private-sector employer in Ventura County, for 11 years. He oversaw the company’s transition from the world’s largest biotechnology company to a blue-chip powerhouse that competes toe-to-toe with some of the most powerful players in Big Pharma.

On Sharer’s watch, Amgen faced repeated questions from federal regulators about the safety of its blockbuster anemia drugs and was forced to change the drugs’ labels. The company also set aside $780 million to settle federal and state charges that it engaged in an illegal kickback scheme, though the settlement is not yet final.

Sharer and Roger Perlmutter, the head of Amgen’s research efforts who is also retiring next year, leave Amgen at a pivotal time in the company’s history. After a decade of consistent profits but lackluster stock performance, Amgen instituted a dividend payment to return profits to its shareholders, who had questioned the company over Sharer’s pay, which amounted to $21 million last year.

Amgen has also found itself squarely in the middle of the national debate over how best to control spiraling healthcare costs. The company must grapple with how to deal with biolosimilars, the biotech analogue of generic pharmaceuticals that are expected to lower costs but eat into the bottom line of firms such as Amgen.

But Amgen recently secured a patent that could give its biggest seller, Enbrel, an arthritis drug that brings in about $3.5 billion a year, protection from biosimilar competition until 2028. It also inked long-term contracts with the nation’s two largest dialysis providers, the biggest buyers of its anemia drugs, that will lock in about two-thirds of the market for those drugs regardless of potential generic competitors.

To facilitate the leadership transition, Sharer will step down as CEO on the same day Bradway takes over but remain on as chairman of the Amgen’s board of directors until the end of 2012.

Sharer, 63, joined Amgen in 1992 and served as president until 2000, when he was named chairman and CEO, the company said in a news release. During that time, Amgen grew from $3.6 billion in revenue with a presence in 17 countries to a company with revenues approaching $16 billion and operations in 55 countries.

Amgen observers have pegged Bradway, 48, as Sharer’s successor for several years as he rotated through various positions to deepen his knowledge of the company. Bradway joined the company as vice president in operations in 2006. He was appointed CFO in 2007 and named president and chief operating officer in 2010. Bradway worked for Morgan Stanley for 19 years before signing on with Amgen.

Amgen also announced that Perlmutter will retire from his position as executive vice president of research and development, effective February 12, 2012. Perlmutter, 59, will continue to work with Amgen as a consultant until February 2013.

Perlmutter, a Montecito resident, joined Amgen in 2000, and during his tenure Amgen has gained the approval for several new drugs.

Sean Harper, the company’s current senior vice president of global development and chief medical officer, will step into Perlmutter’s position. Harper joined Amgen in 2002.