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    Varenicline (Chantix) and cardiovascular problems.
    Jonathan Foulds, PhD posted:
    Today's edition of Canadian Medical Association Journal included a paper on risk of serious adverse cardiovascular events associated with use of varenicline (Chantix) versus use of placebo, in randomized controlled trials of varenicline for smoking cessation. Serious cardiovascular events included things like a heart attack, unstable angina (chest pain caused by lack of oxygen to the heart), and arrythmias). The study used a strong overall methodology by comparing the rates of these events in people given the real drug (varenicline) versus those given an identical pill with no real drug in it (placebo). The main overall, finding was that 1.06% of smokers given varenicline reported a serious cardiac event compared with 0.82% of those given placebo pills. Although these percentages are small, because the analyses included 8216 participants the difference is considered statistically significant.
    Another outcome in the study was "all cause mortality" (death). It was reported that 7/4908 patients given varenicline died (1.4 per thousand) versus 7/3308 of participants given placebo (2.1 per thousand). These numbers were described as too small for proper statistical analysis, but it looks like those tobacco users given placebo were 1.5 times (or 50%) more likely to die in the studies.
    The study appears methodologically strong, but there were a few odd parts in the report. For example, on p7 it states "We found three times the number of serious adverse cardiovascular events among participants in the varenicline group (61/4908 for varenicline v 29/3308 for placebo)." But these numbers clearly show nothing like three times the event rate for varenicline, so I must assume this was either a typo or misinterpretation. The part of the paper I found most persuasive was where the authors pointed out that despite varenicline more than doubling the rate of smoking cessation (which should reduce cardiovascular risks), the varenicline participants still appeared to have a slightly higher rate of cardiovascular events. However, there are two pieces of information I would like to have clarified before coming to a conclusion based on this study. The first is clarification that the analyses were based on the number of patients with cardiovascular events, and not the number of events per se (i.e. to ensure that the same patient was not double counted for different events). The second is clarification on what the event rates were when corrected for time on drug. In most of these studies participants used the drug for 12 weeks or less, but were followed up for 24-52 weeks. If the excess events on varenicline were primarily occurring during the time on drug, that would give me more confidence that this may be a causal effect. If the events were occurring primarily off drug this may make me concerned that the differences might be caused by differential drop-out (the tendency for people receiving placebo, who are less likely to quit smoking, to therefore also be more likely to drop out of the study follow-up and so their cardiovascular events be less likely to be reported).
    Over the next few weeks we will hear responses to this study, hopefully including comments from cardiologists and those investigators involved in the trials. So I would not suggest that people who are using varenicline successfully to quit smoking should immediately rush to stop using the drug on the basis of this study. However, I agree with the study authors that this paper presents solid signs of a potential safety concern that deserves further investigation. An important part of such an investigation will be an analysis of event rates that considers time on drug and the timing of the events.
    Readers should know that I have done consulting work for Pfizer, makers of varenicline, as well as for other companies making smoking cessation medicines.

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