 Ahead of Thursdays meeting of the FDAs Cardiovascular and Renal Drugs Advisory Committee, the agency is raising fresh doubts on the safety of AstraZeneca Plcs NASDAQ: AZN and FibroGen Incs NASDAQ: FGEN anemia drug roxadustat. FDA staffers flagged concerning evidence of blood clotting, when compared with placebo in nondialysis-dependent patients but also when compared against Amgen Inc NASDAQ: AMGN and Johnson Johnsons NYSE: JNJ EpogenProcrit, which is itself known to pose these risks, in dialysis-dependent patients. 