Troubled hearts: antibiotic might fend off second attack. (This Week).

An antibiotic might protect people with heart disease from future coronary events, according to the results of a small-scale trial. The study's limited scope, however, makes its conclusion tentative, some researchers say. They look forward to results of several larger trials now under way.

The new finding fits with a hypothesis that certain infectious organisms are at the root of some heart conditions. Clarithromycin, the antibiotic used in the study, works against Chlamydia pneumoniae. That bacterium is usually associated with respiratory symptoms but may also attack a person's heart. The drug's anti-inflammatory effect may also reduce the risk of further heart problems. Previous studies have suggested that a related antibiotic, roxithromycin, reduces patients' risk of heart problems during treatment, but the effect doesn't persist.

"The action of clarithromycin seems to be long-lasting," says Juha Sinisalo of Helsinki University Central Hospital in Finland.

Sinisalo and his colleagues studied 148 adults, average age 63. Half received clarithromycin tablets daily and half got placebo pills. All subjects had been admitted to hospitals for either unstable angina, a painful condition resulting from inadequate blood supply to heart muscle, or a particular form of heart attack. The researchers treated participants for 3 months and then followed their progress for an average of 18 additional months.

During the treatment period, no clear difference in heart-disease symptoms showed up between the two groups. Over the follow-up period, however, a significant difference appeared in total number of heart-disease episodes, which ranged from unstable angina to death. Only 16 subjects receiving the antibiotic suffered such an event, while 27 placebo-treated subjects experienced one of the negative outcomes. The antibiotic cut overall risk of heart incidents in half, Sinisalo and his colleagues report in the April 2 Circulation.

During follow-up, however, four deaths occurred in the antibiotic-treated group, while no one receiving the placebo died. That worrisome outcome, as well as any apparent benefit from the antibiotic, could be an artifact of the study's small size, says Mark J. Eisenberg, a cardiologist and epidemiologist at the Jewish General Hospital in Montreal.

The study is "encouraging but certainly not definitive," says Eleanor Schron of the National Heart, Lung, and Blood Institute in Bethesda, Md. "I would not treat anyone with antibiotics on the basis of these data."

The seeming persistence of a protective effect, after antibiotic treatment ends, is encouraging, says Joseph Brent Muhlestein, a cardiologist at LDS Hospital in Salt Lake City. However, establishing the magnitude of the benefit--assuming there's a benefit at all--will require data from the much larger clinical trials, Muhlestein says.

He's also concerned that use of antibiotics for heart disease could accelerate the evolution of drug-resistant strains of bacteria. If the risk reduction for heart patients proves to be marginal and they require long-term treatment, "let's not destroy our antibiotic supply," Muhlestein says.