Celebrex (search) more than doubled heart attacks in people enrolled in a cancer-prevention study, Celebrex maker Pfizer said today.

The large study was designed to see whether Celebrex could prevent colon cancer (search) in people who'd had colon polyps (search). Those who took Celebrex had 2.5 times as many fatal and nonfatal heart attacks as those who did not take the drug.

People enrolled in the trial, called the APC trial, are being told to stop taking their study medication.

Another ongoing study looking at whether Celebrex can prevent colon cancer did not find any increased risk of heart attacks in patients taking the drug. This trial, the PreSAP trial, used the same heart measures and the same safety monitoring board as the APC trial.

Celebrex is in the same family of drugs as Vioxx (search). Vioxx was pulled from the market after a colon cancer prevention trial found it increased the risk of heart attacks. Pfizer also makes Bextra, another drug in this family of drugs, called Cox-2 inhibitors.

"Pfizer is taking immediate steps to fully understand the [APC study] results and rapidly communicate new information to regulators, physicians, and patients around the world," Pfizer CEO Hank McKinnell says in a news release.

The APC trial gave patients 400 mg and 800 mg doses of Celebrex per day. People who take Celebrex for arthritis are prescribed doses of 100 mg to 400 mg per day.

The APC and PreSAP trials have enrolled some 3,600 people. Some of them have been taking Celebrex for more than four years.

Pfizer notes that some 2,000 people are enrolled in another study looking at whether Celebrex can prevent Alzheimer's disease in high-risk people. Some 750 of these patients are taking 400 mg of Celebrex daily. As of Dec. 10, this study's safety review board decided to proceed with the study.

Pfizer says it learned of the heart findings from the APC study last night. The National Cancer Institute is conducting the study. An NCI spokesman tells WebMD that the trial's safety monitoring board met until 11:30 p.m. last night.

The impact of the new findings is not yet clear. Celebrex is the ninth best-selling drug in the U.S., with 2003 sales of 2.6 billion, according to Forbes.com.

By Daniel J. DeNoon, reviewed by Michael W. Smith, MD

SOURCES: News release, Pfizer, Dec. 17, 2004. National Cancer Institute. Forbes.com.