Jeffrey B. Kindler, the CEO of the world's biggest drugmaker, stepped down Sunday unexpectedly — after less than five years heading Pfizer Inc., a period in which he reorganized most of the company's operations and made an imprint on the industry.

Jeffrey B. Kindler, the CEO of the world's biggest drugmaker, stepped down Sunday unexpectedly — after less than five years heading Pfizer Inc., a period in which he reorganized most of the company's operations and made an imprint on the industry.

His successor, Ian Read, who has run Pfizer's worldwide pharmaceutical operations since 2006, takes over immediately.

Kindler, a lawyer who joined Pfizer in 2002, revamped its sprawling pharmaceutical sales operation into five divisions that gave their leaders more control and responsibility. Among other successes, that significantly boosted revenue in emerging markets and stabilized sales of older medicines hit by generic competition in the wealthiest countries by promoting them heavily elsewhere.

Kindler also pulled off a huge acquisition that ensures Pfizer remains at the top of the pharmaceutical industry for years to come, buying Wyeth for $68 billion in October 2009. And, as the chairman of the trade group Pharmaceutical Research and Manufacturers of America, he helped line up drugmaker support for the health care overhaul in a deal that ultimately will bring those companies more customers and sales.

In a surprise announcement late Sunday evening, Kindler, 55, said he's leaving Pfizer after 41/2; "extremely demanding" years to recharge his batteries. Kindler said he plans to spend more time with family for a while and prepare for new challenges.