Pfizer said that the reliable science on varenicline (Chantix/Champix), involving more than 14 clinical trials with more than 7,000 smokers, and the medicine’s approval by regulatory authorities around the world, demonstrate the importance of the medicine as an effective and appropriate treatment option for adult smokers wanting to quit. Pfizer stands behind the benefit/risk profile of Chantix.

The company expressed concerns about the reliability of the meta-analysis by Singh et al published today in the Canadian Medical Association Journal (CMAJ). These concerns, among others, are related to the appropriateness of the authors' measure of cardiovascular risk, or composite endpoint, which combines events that do not share a common biological cause; the manner in which cardiovascular events were counted and classified; and a small number of events, which forms the authors' conclusions.

The authors themselves acknowledge that the cardiovascular risk “estimates are imprecise owing to the low event rates.”

Notwithstanding these reliability concerns, the difference of 72 percent reported in the Singh analysis also needs to be put into appropriate context. The actual difference in cardiovascular event rates reported in this analysis was less than one quarter of one percent (i.e., 1.06 percent with varenicline versus 0.82 percent with placebo).

“Pfizer scientists and doctors continuously evaluate the benefits and risks of its medicines, including Chantix,” said Dr Gail Cawkwell, vice president of Medical Affairs. “The currently available safety data on Chantix, including a pooled analysis of clinical data in 7,375 people trying to quit smoking, do not support an increased cardiovascular risk associated with Chantix.”

Pfizer is discussing with the US Food and Drug Administration (FDA) a protocol to conduct a meta-analysis of Pfizer’s clinical trial data to help further evaluate the cardiovascular safety of Chantix. This meta-analysis will address a number of limitations in the Singh analysis; Pfizer expects that it will be based on a more reliable composite endpoint to measure cardiovascular risk, as well as a validated process to classify, or adjudicate, cardiovascular events that are part of the composite endpoint.

Each year, an estimated 5.4 million people worldwide die from smoking related causes, including cardiovascular disease. Chantix is a proven aid to smoking cessation treatment and an important treatment option that has been prescribed to over 13 million patients worldwide.

Chantix is currently approved for use in 99 countries around the world. Pfizer works with regulators worldwide on a continual basis to review and monitor data for Chantix.

Patients should consult with their health care providers to determine what medications are right for them. Patients should contact their healthcare professional if they experience new or worsening symptoms of cardiovascular disease.

Chantix was approved by the FDA in May 2006 as an aid to smoking cessation treatment in adults 18 and older. Chantix has been shown to increase the likelihood of abstinence from smoking for as long as one year compared to treatment with placebo. Adults who smoke may benefit from quit smoking support programmes and/or counselling during their quit attempt.