Shares of Merck & Co. plummet after the company's annoncement that it is pulling Vioxx off the shelves. The company's blockbuster arthritis drug is sold in 80 countries and generates $2.5 billion in revenues. The news sent Merck shares down by more than 25 percent and reduced the company's overall market capitalization by $25 billion. Meanwhile, shares of Pfizer rose. Phizer makes drugs that compete directly with Vioxx. NPR's Jim Zarroli reports.