Two studies released today have turned up new evidence that all of the popular arthritis painkillers known as COX-2 inhibitors may put users at greater risk of heart attacks and strokes.
The first of the two papers published online by the journal Circulation found that patients who had had heart bypass surgery and were taking Pfizer Inc.’s Bextra, in combination with an experimental medication, were three times more likely to have strokes and heart attacks than patients taking a placebo. The statistically significant tripling of the risk showed up when researchers combined the results of two earlier studies involving more than 2,000 people in a statistical technique called a meta-analysis.
A second study found that when mice that are genetically prone to hardening of the arteries were treated with a COX-2 drug and an aspirin substitute, their condition worsened rather than improving, as researchers had anticipated.
Lead researcher Garret A. FitzGerald of the University of Pennsylvania said the two studies led him to conclude that the entire class of drugs poses a risk. He also said that an upcoming clinical trial proposed by Pfizer, the maker of Celebrex, to test whether that drug may help patients with heart disease, should not go forward.
“The clear emergence of a cardiovascular hazard from COX-2 inhibitors in patients, the weak rationale for a study of their protective properties in the first instance, and now this evidence from mice would indicate to me that a trial in high-risk patients, such as that proposed for Celebrex is, at best, ill advised,” said FitzGerald, a longtime skeptic of widespread COX-2 use.
A Pfizer spokeswoman said today that company officials could not comment because they had not yet seen the studies.
The latest bad news for makers and users of COX-2 drugs comes a month before the Food and Drug Administration is scheduled to hold an unusual three-day hearing, from Feb. 16 to 18, of two advisory panels to consider the safety issues that have arisen around the entire class of drugs.
Planning for the meeting began in the fall after Merck & Co. Inc. took its blockbuster COX-2 drug Vioxx off the market after a study it sponsored found heightened cardiovascular risk in volunteers taking the drug. Since then, federal officials have been formally reviewing the risks of using Celebrex in more than 40 government-sponsored studies into other potential uses of the drug. Both Celebrex and Bextra remain on the market, but in increasingly limited use.
COX-2 inhibitors, which are promoted as being less likely to cause gastrointestinal bleeding than other widely used painkillers, were aggressively advertised after they came on the market in the late 1990s. But FitzGerald said that he and colleagues had detected potential cardiovascular problems associated with them even before the drugs were approved by the FDA.
FitzGerald and two colleagues presented preliminary data about the potential heart risks of all COX-2 drugs at an American Heart Association meeting in November, using previously unpublished data from Pfizer studies of Bextra in coronary bypass patients. The first study released today by Circulation is an expanded analysis of that data and comes to the same conclusion that all COX-2 drugs significantly increase the risk of heart attacks and strokes.
The second study, by FitzGerald and Karine Egan, found that deposits of artery-blocking plaque in mice became dangerously unstable after they were given a COX-2 drug and an aspirin substitute.
“We were amazed,” Egan said. “Addition of the COX-2 inhibitor caused changes that, if they occurred in humans, would result in a loss of stability of the plaque, making it more likely to rupture and activate clotting, causing heart attack or stroke.”
FitzGerald acknowledged that tests in mice might not be fully applicable to humans, but he also noted that the earliest evidence of cardiovascular risks associated with COX-2 drugs also came from animal experiments.
The Celebrex study that FitzGerald recommended be scrapped was announced soon after the Vioxx withdrawal as a way for Pfizer to determine whether its COX-2 drugs helped or harmed the heart.
Pfizer said it would test Celebrex against a sugar pill in thousands of people with osteoarthritis and a history of serious heart disease, such as a previous heart attack or severe angina. Patients with known heart problems were excluded from earlier studies of COX-2 drugs, leaving unsettled the question of how the drugs would affect them. In the planned Pfizer trial, patients will be allowed to take supplemental drugs such as aspirin, which is known to lower the risk of heart attack when taken by itself.