Pfizer ( PFE - Get Report) on Monday disputed an allegation by a consumer group that the company hid and downplayed the results of a test of the arthritis drug Celebrex.

The consumer group Public Citizen said the test results hadn't been disclosed, but Pfizer said the results were presented at a scientific conference in 2000 and submitted to the Food and Drug Administration in June 2001. The study, which was monitored by an independent group of safety experts, was never published in a medical journal.

"Pfizer diligently monitors the safety of all its medicines and shares this information with regulatory agencies worldwide," the company said Monday.

The group claimed that its analysis of the data showed "a significantly increased rate of serious cardiovascular adverse events" among patients taking Celebrex than patients receiving placebo.

But Pfizer said the test showed that "definitive conclusions about cardiovascular risk cannot be drawn from this study." In this study, Pfizer noted that Celebrex patients experienced "more cardiovascular events than patients taking a placebo. However, Celebrex patients "were up to four times more likely to have key cardiovascular risk factors" vs. the placebo patients, thus impairing the findings.

Public Citizen said its analysis of test data reaffirmed its belief that Celebrex should be banned. Last week, the consumer group asked the FDA to ban both Celebrex and Bextra, another Pfizer arthritis drug. The group reiterated its request in a Jan. 31 letter to the FDA, containing its comments about the Celebrex study.

Both Celebrex and Bextra belong to the class of drugs called COX-2 inhibitors. That's the same drug class that contains Vioxx, the arthritis drug that Merck ( MRK) pulled from the market on Sept. 30 after a Merck-sponsored test showed patients that patients taking Vioxx for more than 18 months had a higher risk of cardiovascular problems than did patients receiving a placebo.

The Food and Drug Administration has scheduled three days of advisory committee hearings in mid-February to examine all COX-2 drugs, including Merck's Arcoxia and Pfizer's Dynastat which are available in many foreign markets but not yet approved in the U.S. Another COX-2 drug awaiting FDA review is Prexige from Novartis ( NVS).

The hearings were sparked partly by the Vioxx withdrawal and partly by a series of perplexing research results involving Bextra and Celebrex. In recent months, each drug has been the subject of one test showing increased cardiovascular risk. But other tests have shown no statistically significant differences between patients taking the respective drugs and patients taking a placebo.

The latest dispute involving Celebrex focuses on a phase II test -- the second in a series of three clinical trials required for regulatory approval. In that case, Pfizer was testing whether Celebrex would be an effective treatment for Alzheimer's disease. The study ran nearly two years, from July 1, 1997, through June 24, 1999, in 30 centers in the U.S. and Europe, testing 425 people. One group was given Celebrex; the other group was given a placebo. Patients were evaluated after 12 months.

The researchers said the survey had qualifications: The sample size was small, the patients had complicated medical histories and the Celebrex patients entered the study with more cardiovascular risks than did the placebo patients.

Researchers concluded that the safety of Celebrex vs. placebo "in this elderly, debilitated population cannot be decisively concluded." They also said the drug wasn't effective as an Alzheimer's disease treatment.

The test's conclusions also provided some apparently contradictory comments. For example, the report said "individual cardiovascular events did not differ significantly between the celecoxib and placebo treatment groups." Celecoxib is the generic name for Celebrex.

However, in the next sentence, the researchers said: "A statistically significant difference in adverse events was observed for certain cardiovascular-related body system terms."

Public Citizen said it examined the data and concluded that patients taking Celebrex had a 3.6 times increased risk of "serious cardiovascular adverse events." Public Citizen reached its conclusions by analyzing "a composite of all cardiovascular events" rather than relying on the results for individual events. Such events included stroke, chest pains, heart failure, irregular heartbeats and heart attack.

"The FDA must act immediately to protect people from these two dangerous drugs," said Dr. Sidney Wolfe, director of Public Citizen's Health Research Group, in his Jan. 31 letter to the FDA.

On Monday, Pfizer's stock lost 19 cents, or 0.8%, to $24.16.