Coronary heart disease (CHD) is the single largest killer of Americans. CHD is an umbrella term for many conditions that affect that heart including heart attack , angina pectoris (severe chest pain), and atherosclerotic cardiovascular disease . In the US in 2002, CHD caused one of every five deaths. In fact, about every 26 seconds an American suffers a coronary event and about every 60 seconds, someone dies from one.

Many risk factors for CHD—such as smoking, eating a high-fat diet, and not exercising enough—are well known. But because many people with CHD have none of these well accepted identified risk factors, clinical studies continue to look for unidentified factors that may contribute to CHD. Bacterial infection has been implicated in the development of CHD. One bacterium in particular, Chlamydia pneumoniae , has been associated with a doubling of the risk of atherosclerotic lesions and heart attack.

Because this bacterium has been discovered within atherosclerotic lesions, it stands to reason that antibiotic treatment (which is used to kill bacteria) might have a positive effect on the development of CHD. Initial studies using antibiotics reported that antibiotic therapy might lead to a reduction in risk, but others studies have failed to confirm a benefit.

A study published in the April 21, 2005 issue of the New England Journal of Medicine evaluated the effect of one year of azithromycin treatment on the prevention of coronary events in people who had stable CHD. Azithromycin (Zithromax®) belongs to a class of drugs called macrolide antibiotics and is effective in treating infections caused by Chlamydia pneumoniae .

About the Study

The study involved more than 4000 men and women, average age of 65, who had stable CHD. These participants were randomized to receive either 600 milligrams of azithromycin or a matching placebo tablet once weekly for one year.

The primary endpoint of the study was the first occurrence in a patient of any of the following: death due to CHD; a nonfatal heart attack; surgical procedure to reestablish blood supply to the heart; or hospitalization for unstable angina. Secondary endpoints included stroke, carotid endarterectomy (removal of the inner lining of a clogged artery), and cardiac collapse followed by resuscitation.

During the first year, participants were interviewed at three and six weeks and then every three months to discuss if they were taking the medication weekly, if they were experiencing any side effects, and it there had been any endpoint events. For the remainder of the study, which averaged almost four years, participants were interviewed every six months.

The Findings

The results showed that the cluster of events defined as the primary endpoint occurred with almost the same frequency for the azithromycin group and the placebo group. In fact, the frequency of the primary endpoint occurring was 22.3% in the azithromycin group and 22.4% in the placebo group. Additionally, there was no difference between the two groups for any individual endpoint occurring, whether it was primary or secondary.

The azithromax group experienced a slightly higher rate of gastrointestinal symptoms (nausea, abdominal pain, and diarrhea) as well as hearing loss as compared to the placebo group.

Another study published in the same issue of the New England Journal of Medicine also came to the same conclusion. In this study, more than 4000 participants who had been hospitalized for acute coronary syndrome were randomized to receive 400 milligrams gatifloxacin, an antibiotic known to be effective against Chlamydia pneumoniae , or placebo. Participants took the antibiotic for 10 days every month for an average of two years. Just like the previously study, no reduction in the rate of cardiovascular events was observed for the group taking gatifloxacin.

How Does This Affect You?

Although these results are compelling, this study does have some limitations. The participants in both studies already had preexisting heart conditions—perhaps, an antibiotic might help stave off coronary events if it was given to people before they develop heart disease.

Also, the possibility exists that the treatments were not continued long enough or that the dose was too small. Should we interpret the studies’ results to mean if we just take more for longer, it may reduce the risk? No. Taking antibiotics for prevention of coronary events in the absence of clear proof of a benefit is a risk that is not yet worth taking. Long-term antibiotic use can lead to an increase in antibiotic-related side effects. Additionally, there is the possibility that the bacteria will develop a resistance to the antibiotic taken.

Since science has yet to find adequate support for antibiotic use to prevent coronary events, it is best to stick with what we already know works—getting plenty of exercise, eating healthfully, and not smoking.