Pfizer, the world's biggest drugmaker, has named Ian C Read chief executive officer of the company after former head Jeffrey Kindler announced his unexpected retirement.
Read (57) currently runs the company's global biopharmaceutical businesses, and the board would select a new non-executive chairman from among its members within two weeks.
Announcing his retirement, Kindler said in a statement that the "24/7 nature of my responsibilities" had been "extremely demanding", especially after last year's $67bn (£42bn) takeover of Wyeth, adding that he was leaving to "recharge my batteries".
Since taking over as CEO of the company in 2006, Kindler has seen the company's shares fall 27 per cent.
Tim Anderson, an analyst at Sanford Bernstein, pointed out, "The departure is sudden but I doubt there was one event per se that caused Kindler's retirement. It is highly likely he was pushed."
Les Funtleyder, portfolio manager of the Miller Tabak Healthcare Transformation Fund, also said it was unusual for a CEO to resign citing fatigue and hinted that Kindler's resignation may be more connected to Pfizer's poor stock price performance.
With Pfizer set to lose patent protection in the US next year for Lipitor, the company needed new blood to power its further growth, the analysts said, and predicted that the shares will rise as a result of the change.