AstraZeneca PLC announced today its cholesterol drug Crestor failed to beat its top rival from Pfizer Inc., Lipitor, in a study meant to prevent clogged coronary arteries in patients, sending the company's shares down.

Shares of Astrazeneca fell 2.74 percent or 1.28 dollars to $45.41 a share during midday trading on the New York Stock Exchange after the release of the results of the SATURN study.

Crestor didn't show a "statistically significant" reduction in the volume of plaque in the arteries that feed blood to the heart, according to the SATURN study.

"The results for the primary efficacy measure, which was change from baseline in percent atheroma volume (PAV) in a ≥40 mm segment of the targeted coronary artery as assessed by intravascular ultrasound (IVUS), demonstrated a numerically greater reduction in favor of CRESTOR versus atorvastatin but did not reach statistical significance" said the company in a press release.

Lipitor is the world's top selling drug nearly at $11 billion a year. Astrazeneca was seeking to show that its Crestor drug was more effective than generic Lipitor ahead of its availability on November 30.

The generic medicine could cost less than half the price of the original Lipitor.