It thought it could use Medco, which is hired by managed-care firms to fulfill drug purchases for patients, to increase the sales of its own drugs. But Merck-Medco's margins remained paper-thin even as its revenues grew fold, crimping the margins of the entire company. With its thin margins and ballooning size, Merck-Medco may have just been too much of a drag on Merck's share price and a distraction from Merck's core business of producing blockbuster drugs. Merck lost its spot as the world's biggest drugmaker. Now, its drug business is being forced to turn on a dime to save itself.