For the second time in four weeks,

Pfizer

(PFE) - Get Report

has announced results of a company-sponsored test showing that its blood pressure drug Norvasc does a better job against competing therapies.

On Wednesday, Pfizer said early results from a clinical trial involving 20,000 patients showed that patients receiving Norvasc-based therapy experienced greater cardiovascular benefits than patients receiving a standard blood-pressure therapy. The results were powerful enough that the independent group supervising the test decided to halt the clinical trial early.

"The early stopping of this trial clearly confirms the benefits of blood-pressure lowering with a Norvasc-based regimen" for patients with high blood pressure and "additional cardiovascular risk factors," said Dr. Joseph Feczko, president of worldwide development at Pfizer, in a prepared statement.

Pfizer didn't release any data. "We look forward to receiving the fully analyzed results," Feczko said. According to

Reuters,

the study's principal investigator said the results will be made available during a cardiology conference in March and published later next year in the British medical journal

The Lancet.

The announcement helped boost Pfizer's stock, which gained 28 cents, or 1%, to $27.48.

The clinical trial, nicknamed ASCOT, looked at two groups of patients. One group received Norvasc, which belongs to the class of drugs called calcium-channel blockers, and, if necessary, two other hypertension drugs -- an ACE inhibitor and an alpha blocker. The other group received another blood pressure drug called a beta blocker and, if necessary, a diuretic and an alpha blocker.

The findings are important for Norvasc, which has been on the market for 14 years, because Pfizer is trying to extend its sales life by combining it with the cholesterol drug Lipitor to create the combination pill Caduet. Norvasc's U.S. patent expires in September 2007.

For the first nine months, Norvasc produced $3.2 billion in sales, making it the company's second-best selling drug behind Lipitor, which accounted for $7.6 billion. Caduet's sales were only $35 million. The FDA approved the drug 11 months ago.

The ASCOT study has been going on since 1998, measuring the heart health of people in seven European countries. Two years ago, the cholesterol portion of ASCOT was halted early after results showed that Lipitor patients had a "significant benefit" in the reduction of heart attacks and strokes.

Four weeks ago Pfizer said another study, nicknamed CAMELOT, demonstrated that patients receiving Norvasc had

fewer cardiac problems than patients receiving standard care, which includes aspirin and cholesterol drugs. The study was published in the

Journal of the American Medical Association.