Pfizer

(PFE) - Get Report

said Tuesday that clinical trials of two experimental drugs produced favorable results for reducing the risk of heart disease.

One of those drugs, torcetrapib, is being tested in combination with Lipitor. Torcetrapib is designed to improve so-called good cholesterol while Lipitor reduces bad cholesterol, and a combination pill is crucial to Pfizer's

extending its cholesterol franchise.

The other drug is varenicline, a smoking-cessation drug. Pfizer says smoking doubles the risk of cardiovascular disease and triples the risk of death by heart attack. Clinical trial results were released Tuesday at the annual meeting of the American Heart Association in Dallas.

Pfizer said two midstage clinical trials of the torcetrapib-Lipitor combination showed that an increase of good cholesterol by 44% to 66% and a decrease of bad cholesterol by 41% to 60% among some 500 patients.

"These results were pivotal in our decision to move forward with a Phase 3

clinical trial program, the final stage in clinical development," said Dr. Joseph Feczko, Pfizer's chief medical officer in a prepared statement. "If this program is successful, this new approach could change the way physicians manage cholesterol and reduce further the risk of atherosclerosis in their patients."

Pfizer says its combination pill research is the largest clinical trial program in its history, covering some 25,000 patients "at hundreds of medical centers worldwide at a cost of about $800 million."

If the late-stage clinical trials are successful, many analysts say the combination pill could be available in the U.S. by 2008, helping preserve the Lipitor cholesterol franchise that provided $10.9 billion in sales -- and 24% of corporate revenue -- last year.

Lipitor's main U.S. patent expires in 2011, assuming that Pfizer survives a challenge by the Indian generic drugmaker

Ranbaxy Laboratories

. A federal court judge's ruling is

expected later this year or early next year.

The smoking-cessation drug, varenicline, won't produce as much revenue, but it should get to the market several years ahead of the combination cholesterol drug. Earlier this month, Pfizer submitted applications to the Food and Drug Administration and the European Union for the drug whose brand name will be Champix.

The applications were backed by late-stage clinical trials that showed Champix performed better than the only prescription antismoking pill on the market, Zyban from

GlaxoSmithKline

(GSK) - Get Report

.

In two studies involving around 2,000 smokers, patients received either Champix, Zyban or a placebo for 12 weeks of treatment. Then they were monitored for another 40 weeks without treatment.

Pfizer said the quit rate for Champix patients was 44% after 12 weeks. That's a significant improvement over the 30% quit rate for Zyban patients and 18% for placebo recipients.