An analysis of more than a dozen drug studies finds that smokers who take the drug Chantix to help them kick the habit face significantly higher risks of cardiovascular problems including stroke, heart rhythm irregularities and heart failure, along with other serious side effects.
The drug’s maker, Pfizer, says it's too early to draw conclusions from the data and that more studies are needed.
The study reviewed the data from 14 clinical trials of Chantix. It found a 72-percent increase in the risk of cardiovascular incidents among smokers who took the quit-smoking aid compared to those who received a placebo or sugar pill. Researchers evaluated information collected on 8,200 smokers from around the world who did not have heart disease when the studies began.
The studies were submitted to US drug regulators as part of Pfizer’s application for approval.
Sonal Singh, professor of medicine at Johns Hopkins University School of Medicine in Baltimore, Maryland, was a lead author of the study.
Overall, Singh says, there was a 1.06 percent increased risk of heart problems among study participants who took the smoking cessation drug compared to a .82 percent risk of cardiovascular disease in the placebo groups that were followed by Pfizer for one year after they stopped using Chantix.
While the difference in risk may not sound significant, Singh says the impact is great if you consider the number of users in the US and nearly 100 countries worldwide where Chantix has been approved as a quit-smoking aid.
"If you look at the (US) population, there were more than three million users of Chantix," says Singh. "So, even a small fractional increase in relative risk of heart attack translates into thousands of heart attacks in the United States. And if you look at 13 million users of Chantix worldwide even that quarter of a percent risk - you’re talking about thousands of lives.”
The heart problems began to show up as early as one year after the volunteers completed a 12-week course of treatment with Chantix.
“My main reaction is that this will be distressing news for patients who are trying to quit smoking on their own and finding it very, very difficult," says Gail Cawkwell, vice president of medical affairs for Pfizer.
Cawkwell acknowledges a small increase in the risk of heart problems among Chantix users, saying the company will work with the federal approving agency - the US Food and Drug Administration (FDA) - to figure out what’s going on.
“I think it’s also important to recognize that the kind of cardiovascular events are a mixture of events that can be caused by lots of different things," says Cawkwell. "So we’re really looking closely at this data, all of our own data, and working with the FDA to do an analysis that will hopefully give us important information about the cardiovascular safety profile of Chantix.”
Chantix contains what are called black box warnings stating that the drug causes changes in behavior and mood, including suicidal thoughts and actions.
Cawkwell says the company will likely add a warning about cardiovascular problems to the black box.
Curt Furberg, professor of public health and Sciences at Wake Forest University in Winston-Salem, North Carolina, also co-authored the report on Chantix.
He blames the problems with Chantix and other medications on an inadequate drug review process in the US.
“It involves few patients and if you don’t look for suicides or violence or heart attacks, you don’t find it," says Furberg. "And the companies are not eager to discover problems in the pre-approval process. So, it’s all detected after approval.”