Azithromycin weekly for one year does not reduce the risk of myocardial infarction or other adverse coronary event in patients with stable coronary artery disease, according to an article in the April 21st issue of the New England Journal of Medicine.

Previous studies have found Chlamydia pneumoniae in arterial plaque of patients with coronary artery disease. Some doctors have reasoned that removal of C. pneumoniae from the system could reduce the risk of subsequent cardiac events. Prescription of antibiotics for this purpose had not been tested through a randomized clinical trial. The investigation of whether antibiotics could be used to treat the bacteria, and therefore reduce the risk of cardiac events, was conducted at 27 different sites in the United States.

The current study, called the Azithromycin coronary events study, or ACES, found no benefit from treating C. pneumoniae bacteria with an antibiotic in order to reduce the risk of myocardial infarction or improve overall cardiac outcomes.

ACES researchers randomly assigned 4,012 men and women to receive either once-weekly doses of azithromycin or placebo for one year, starting in 1999. After an average follow-up of 3.9 years, there was no significant reduction in cardiac events, defined as death, myocardial infarction, unstable angina, angioplasty or cardiac surgery, among participants receiving antibiotic compared with those given placebo. This lack of antibiotic effect was shown for all participants, regardless of age, gender, smoking status, or presence of C. pneumoniae antibody. Antibiotic treatment also had no effect on total mortality or on incidence of stroke.

Men and women were included in the study if they had stable coronary artery disease following a previous cardiac event such as myocardial infarction, angioplasty, or cardiac bypass surgery. Azithromycin was selected because of its proven effectiveness against C. pneumoniae and for its once-weekly dosing.

“This is conclusive evidence against using antibiotics to treat late stages of cardiovascular disease, but since the trial was not designed to study the role of C. pneumoniae in causing coronary heart disease, the ACES results do not tell us anything about a possible role of C. pneumoniae in the early development or acceleration of disease in the coronary arteries,” said the study’s principal investigator and lead author, Dr. J. Thomas Grayston, professor of epidemiology in the University of Washington School of Public Health and Community Medicine. “More study is needed to determine the role of C. pneumoniae in heart disease.”