Summary Box: Crestor study backfires on maker

THE GAMBLE: British drugmaker AstraZeneca PLC, hoping to avert a big drop in sales of top seller Crestor when generic versions of rival cholesterol drug Lipitor arrive, funded a two-year patient study aiming to show Crestor was better at reducing plaque in heart arteries.

THE RESULT: The study found the two drugs are about equally effective.

THE IMPACT: Analysts said the study, the first comparing Crestor directly to a competing drug, will add to pressure on Crestor sales once generic Lipitor versions hit in the U.S. on Nov. 30.