Pfizer says a study found an increased risk of heart problems with the painkiller Celebrex. The news comes after another painkiller, Vioxx, was withdrawn from the market. Like Vioxx, Celebrex is in a class of drugs called COX-2 inhibitors. Pfizer does not plan to pull Celebrex from the market. Hear NPR's Steve Inskeep and NPR's Richard Knox.