WASHINGTON, Dec. 22 - AstraZeneca's recent full-page newspaper advertisements defending the safety of its cholesterol-lowering pill, Crestor, are "false and misleading," in part because serious concerns remain about the safety of the drug, federal drug regulators said Wednesday. The advertisements stated that "the F.D.A. has confidence in the safety and efficacy of Crestor" and that the agency "as recently as last Friday publicly confirmed that Crestor is safe and effective." Neither is true, said a letter from the Food and Drug Administration to AstraZeneca. In fact, days before the advertisements ran, top agency officials were widely quoted expressing concerns about...