MONDAY, July 4, 2011 (HealthDay News) -- The quit-smoking drug Chantix may increase the risk of heart attacks and strokes by as much as 72 percent in smokers who take it, even those without heart disease, researchers say.
The new study comes just over a week after the U.S. Food and Drug Administration reported a small but significant risk of heart attack and stroke among people with pre-existing heart disease using Chantix (varenicline).
"All smokers who take Chantix are at risk for heart attack, stroke or other cardiovascular event," said study author Dr. Sonal Singh, an assistant professor of general internal medicine at the Johns Hopkins University School of Medicine in Baltimore.
The findings, published July 4 in CMAJ (Canadian Medical Association Journal), are based on a review of 14 studies involving more than 8,200 smokers or users of smokeless tobacco, most of whom had no evidence of heart disease. About 4,900 took Chantix; the others were given a placebo. Follow-up ranged from 7 to 52 weeks.
The researchers found that 52 (1.06 percent) of the participants taking Chantix had serious cardiovascular events compared with 27 (0.82 percent) of those taking the placebo.
"Chantix is causing the problems it's supposed to prevent," Singh said, noting that, in addition to certain cancers, smoking increases heart risks. "Don't use Chantix, and try to quit unassisted," he said. "If you can't, there are other cheaper and safer alternatives."
Another study author, Dr. Curt D. Furberg, a professor of public health sciences at Wake Forest University Baptist Medical Center in Winston-Salem, N.C., said they found that the risks associated with Chantix outweigh any potential benefits.
"Chantix can cause cardiovascular problems, and this is on top of other bad news about the drug," he said. The FDA in 2009 mandated that Chantix carry a "black-box" warning about the potential risks of psychiatric problems, including depression and suicidal thoughts.
Chantix is not that effective in helping people quit smoking, he said. "If 10 people start on the drug, nine are back smoking after one year," he added. "The benefit is modest at best."
But pharmaceutical giant Pfizer, the maker of Chantix, shot back that the drug is a valuable tool for would-be ex-smokers, and the authors' conclusions are flawed.
"Pfizer disagrees with the interpretation of the data," the company said in a statement. "The analysis contains several limitations; most notably that it is based on a small number of events, which raises concerns about the reliability of the authors' conclusions. The authors acknowledge that their risk 'estimates are imprecise owing to the low event rates.' The actual difference in cardiovascular event rates seen in the Singh analysis was less than one-quarter of one percent."
The authors do acknowledge some limitations with their study, including the small number of heart problems overall. But they advised doctors to consider the potential cardiovascular and psychiatric problems before prescribing Chantix.
However, Dr. Bruce Darrow, an assistant professor of cardiology/medicine with the Mount Sinai School of Medicine in New York City, urged caution before jumping to any conclusions about Chantix's future.
"There is not enough evidence to conclude that Chantix is unusable or too dangerous to use, but there is enough evidence to suggest there is that possibility," Darrow said.
And Pfizer said that it "works with regulators, like the U.S. Food and Drug Administration (FDA), on a continual basis to review and monitor data for Chantix. In particular, we are working with FDA to conduct a combined analysis of clinical trial data (meta-analysis), which will help further evaluate the cardiovascular safety of Chantix."
Darrow said that if you are already taking Chantix, you should discuss what the CMAJ study means with your doctor and ask whether or not you should continue. Never stop taking any medication without first discussing it with your doctor, he said.
Data on Chantix is only available for up to 52 weeks. "We know that a lot of long-term benefits of stopping smoking are not seen at this point, so if people who use Chantix are followed for a longer time, we may see more benefits," Darrow added.
"I would be reluctant to give Chantix out of the gate, but there may be some patients who can't quit using other methods who go into it with their eyes open," he said. "There may be a potential for a small risk of heart disease in the short term, but the three-year risk of heart disease may go down and the long-term risk of lung cancer goes down," he pointed out.
Jeff Stier, a senior fellow at the National Center for Public Policy Research, a Washington, D.C.-based conservative think tank, said this study isn't the final word. "You need a study that compares any increased risk of a cardiovascular event with Chantix to risk seen among those who continue smoking," he said.
"This study underscores the fact that helping people quit smoking is not a risk-free endeavor," he added.
For more information on heart disease, visit the U.S. National Library of Medicine.