Pfizer sought to reassure investors yesterday that the unravelling of its "monolithic" structure would prepare it for the impending expiry of the patent for its blockbuster cholesterol drug Lipitor, worth some $12bn in annual sales.

Under pressure from Wall Street to retool Pfizer to boost sales and profit, Jeff Kindler, chief executive, gave a frank assessment of the disruption created by its $90bn Warner-Lambert and $60bn Pharmacia deals since 2000. He provided the most detailed evidence yet of Pfizer's efforts to streamline its operations, change its culture and improve its research and science.