Pfizer Inc. (PFE) shares rebounded Tuesday as a study of Alzheimer's patients found that its arthritis drug Celebrex carried no increased cardiovascular risks, differing from findings of a study in cancer patients released last week.

Pfizer has lost about $30 billion in market capitalization since Friday, when a large cancer-prevention study showed that large doses of the drug more than doubled the risk of heart attack. The Alzheimer's study released on Monday eased investors fears that U.S. regulators will force Pfizer to withdraw Celebrex, sending its shares up more thanthdrawal of Celebrex (search) and Bextra (search) is likely to lead to upside, and this news, in our view, is a catalyst to get the ball rolling," said Mara Goldstein, an analyst at CIBC World Markets, in a research report.

But while Celebrex fears were eased, confusion over the safety of painkillers in general was heightened as the same trial showed that patients taking naproxen (search), sold over the counter as Aleve, had a 50 percent increase in heart risk.

Multibillion dollar painkillers have come under increased scrutiny since Merck & Co. Inc. (MRK)withdrew its arthritis drug Vioxx from the market in late September after it showed an increased risk of heart attack and stoke in long-term users.

Pfizer's Celebrex and successor drug Bextra are in the same class, known as COX-2 inhibitors (search), as Vioxx, and many critics have claimed the risks associated with Vioxx could also be linked to other members of the class.

Even if Celebrex remains on the market, however, sales are likely to fall.

"While we still believe that use of COX-2s will decline and place pressure on earnings per share, we are less inclined to think that a broad-based withdrawal is likely," Goldstein said.

Pfizer said in a statement that the results of the 2,500-patient National Institutes of Health Alzheimer's study, in which patients took 400 milligrams daily, were consistent with the large body of evidence about the safety of Celebrex already accumulated.

"This is important new information that should be considered by doctors and patients as they evaluate the various treatments for arthritis and pain," said Hank McKinnell, Pfizer's chief executive officer.

Still, Pfizer isn't necessarily out of the woods, analysts said. The acting head of the U.S. Food and Drug Administration, Lester Crawford, said it is premature to say what the agency is going to do about either Celebrex or Aleve, and analysts said the Alzheimer's trial has just made the agency's job harder.

"At the end of the day I think this is a good outcome for Pfizer," said Scott Henry, an analyst at Oppenheimer & Co. "It doesn't make the problems go away; this is just one data point among many, but this data point was more favorable than not."

Pfizer's shares rose 78 cents, or 3.2 percent, to $25.07 on the New York Stock Exchange.