NEW YORK (Reuters Health) – A review of past research concludes that people taking Pfizer’s smoking-cessation drug Chantix (varenicline) do not have a higher risk of heart attacks and other serious heart problems as was reported by a study last year.
The current paper’s authors say last year’s study could harm people by alarming them to the point of stopping their use of the drug.
“The initial study that came out was misleading. The findings were inflated and they were just focusing on that relative risk. It caused confusion,” said Dr. Judith Prochaska, of the Center for Tobacco Control Research and Education at the University of California, San Francisco.
For the new study, Dr. Prochaska and a colleague analyzed the 22 randomized controlled trials published since information on varenicline first became available in 2005.
The trials included a total of 9,232 people. Treatment typically lasted three months, and the researchers followed the participants for a month after they stopped taking the drug
Of the 5,431 people who took Chantix, 34 — about 0.63% — had a serious heart problem. In the comparison group, 18 of 3,801 people — about 0.47% — had a problem.
The researchers wrote May 3rd in BMJ that the drug is “neither clinically nor statistically” associated with an increased risk of heart problems.
Last year’s study, published in the Canadian Medical Association Journal, reviewed 14 randomized controlled trials that ranged in length from seven weeks to a full year. (See Reuters story of July 4, 2011.)
Overall, that study looked at data on 8,216 people. Among those taking Chantix, about 1.06% had a serious heart problem, vs about 0.82% in the control groups.
“The results are essentially similar. There is a difference of interpretation,” said the lead author of last year’s study, Dr. Sonal Singh of Johns Hopkins University School of Medicine.
There were some key differences between the two reports, even though each set of researchers reviewed many of the same studies.
The most striking difference was how long the participants were followed. Last year’s report followed some people for up to a year, whereas the new report stopped tracking serious heart problems a month after Chantix was stopped.
Dr. Prochaska and her colleague said they used a shorter follow-up in order to exclude heart problems that may have been caused by patients’ history of smoking.
For example, one of the studies used in both reports reported four heart problems over a year in the group taking Chantix. The new report only counts two of those.
The conflicting results show that statistics can be used or misused to misinterpret a situation, said Dr. Jonathan Whiteson, director of cardiopulmonary rehabilitation at NYU Langone Medical Center in New York.
“If you input something that doesn’t make sense, what comes out won’t make sense,” said Dr. Whiteson, who was not involved in either of the analyses.
He told Reuters Health that it’s important for doctors not to change their practice based on one report until there is additional data to support it.
Chantix is one of three methods approved by the U.S. Food and Drug Administration to help smokers quit; the others are the prescription drug buproprion (Zyban, Wellbutrin) and over-the-counter nicotine replacement products like patches and gum.
Chantix is a “partial agonist,” meaning it works by both blocking and partially stimulating some of the same cell receptors that respond to nicotine. It is the first drug that intentionally targets those receptors to come to market.
The Chantix label carries a so-called black box warning about the possibility of psychiatric events, including depression and thoughts of suicide. The label also warns that serious heart problems have been seen in people taking Chantix.
Pfizer told Reuters Health in a statement, “Given the significant public health risks of smoking, Chantix is an important treatment option for adult smokers who want to quit. Patients should consult their doctor to determine what treatment option is right for them.”
Dr. Prochaska is involved with a clinical trial partly funded by Pfizer, but she told Reuters Health the drug company was not involved in the current analysis of Chantix trials.