DALLAS (CNN/Money) - Pfizer failed to prove that Lipitor, its top-selling cholesterol reducer, does a significantly better job in reducing fatal heart attacks that Merck's cholesterol-cutting Zocor, the company said at the American Heart Association conference Tuesday.

The news triggered a drop in Pfizer (Research)'s stock price.

But Pfizer had better news from a separate study, showing that its experimental anti-smoking drug varenicline works better than Zyban, the only anti-smoking prescription pill on the market.

A Pfizer-funded, five-year study failed to reach its primary goal and showed that Lipitor was only 11 percent better than Zocor in reducing sudden death heart attacks, the company said, but this difference is not considered "statistically significant."

Dr. Terje Pederson, director of the study and professor of medicine at Ulleval University Hospital and director of the Center for Preventative Medicine in Oslo, Norway, said the results of the study showed, "the benefits were more modest than we expected."

Although Pfizer's study couldn't prove Lipitor does a significantly better job reducing fatal heart attacks than Zocor, the study which concluded in March, achieved its secondary goals, including finding that Lipitor reduces all cardiovascular events, such as heart attacks and strokes by 16 percent over Zocor, according to Pfizer scientist Dr. John Tsai, worldwide medical team leader for Lipitor.

Lipitor sales totaled $10.8 billion for Pfizer in 2004 and that tally is expected to increase this year. The patents for Lipitor are not expected to expire until 2010 or 2011. But the patent for Zocor, which totaled $5.2 billion in 2004 sales for Merck, is expected to run out next June.

Normally a drug's patent expiration causes a price plunge. When asked if he was concerned that Lipitor patients would flock to a cheaper generic form of Zocor, Tsai didn't express concern because he said Lipitor is better than Zocor in reducing the risk of heart disease.

The anti-smoking drug, varenicline, works by blocking the pleasurable effects of nicotine in addicts and reduces the craving and withdrawal symptoms associated with quitting, said Dr. Serena Tonstad, head physician at the Department of Preventative Medicine at Ulleval University Hospital and a professor at the University of Oslo, who conduct the studies and presented Pfizer's findings to reporters.

"This is the first non-nicotine drug that has been specifically designed for smoking cessation," said Tonstad. "So this is really history."

Pfizer conducted two smoking cessation studies involving 2,000 smokers who averaged one pack a day. Both studies resulted in "quit rates" of 44 percent for varenicline, 30 percent for GlaxoSmithKline's Zyban, and 17.7 percent for placebo after 12 weeks, the company said.

Smokers took the drugs for one week while smoking and then were forced to quit smoking on day eight, said Tonstad. Taking even a single puff after day 7 was considered a failure for smoking cessation, and carbon monoxide was measured in the breath to confirm whether test participants were smoke-free, said Tonstad.

Tonstad continued to study participants after 12 weeks when they stopped taking the drug. After the patient had stopped taking the drugs the 52-week study showed that the quit rate dropped between weeks 13 and 52, to 22.1 percent cessation for varenicline, 16.4 percent for Zyban, which is also known as bupropion, and 8.4 percent for placebo.

Pfizer submitted varenicline to the Food and Drug Administration this month and, if it's approved, intends to market the drug under the name Champix. Tonstad said the drug was considered safe.

Pfizer also announced the results of separate studies combining Lipitor with an experimental drug, torcetrapib, showing that the combination effectively raised HDL, or "good" cholesterol, and reduced LDL, or "bad" cholesterol.

The phase 2 studies, which are conducted prior to phase 3, or late-stage clinical trials, showed that the Lipitor-torcetrapib increased HDL cholesterol by 44 to 66 percent, and reduced LDL by 41 to 60 percent, the company said.

"We think this is going to be the first breakthrough in lipid therapy in 20 years," said Dr. Chuck Shear, Pfizer's vice president of cardiovascular metabolic development. "It's going to provide very significant risk reduction."

Pfizer is currently conducting phase 3 studies on the combination. Shear would not say when the late-stage studies are expected to be completed. If phase 3 is successful, the next step would be filing with the FDA.

Michael Krensavage, analyst for Raymond James, recently estimated that, under the best case scenario, annual sales of a Lipitor-torcetrapib combination could reach $25 billion.