Pfizer Inc. said on Tuesday its experimental cholesterol drug torcetrapib, combined with its multibillion-dollar selling cholesterol drug Lipitor, significantly increased levels of “good” cholesterol while significantly lowering “bad” cholesterol.

The world’s biggest drug company said results of two mid-stage, or phase II, studies presented at the annual meeting of the American Heart Association in Dallas were promising enough that the company will continue into the final stage of the expensive development process.

Pfizer views torcetrapib as its most important experimental product and hopes it will succeed from Lipitor, the world’s biggest-selling drug with annual sales of nearly $12 billion, when it loses patent protection in 2011.

In a study of nearly 500 patients, those who received 60 milligrams of torcetrapib and either 10, 20, 40 or 80 milligrams of Lipitor, saw their heart-protective good cholesterol rise between 44 percent and 66 percent, Pfizer said.

At the same time their bad LDL cholesterol fell between 41 percent and 60 percent.

While torcetrapib lowered LDL cholesterol, prior studies showed that the effect is greater when combined with Lipitor, the New York City-headquartered company said.

The company said patients taking 60 milligrams of torcetrapib with Lipitor saw an increase in systolic blood pressure, which will be studied and analyzed further in the phase III studies.

Torcetrapib is designed to block a protein in the blood known as CEPT that is responsible for transferring cholesterol from its “good” HDL carrier to the “bad” LDL carrier of cholesterol that results in the buildup of plaque in arteries of the heart.