The bacteria can double the chance of developing subsequent heart attacks, and researchers thought antibiotics might help cut that risk.

But one study, in which Pfizer’s Zithromax, or azithromycin, was compared to a placebo in 4,012 heart disease patients found that the antibiotic — even if given over a year — had no effect on the rate of death, heart attack, or other gauges of worsening disease.

In a second study, 4,162 volunteers received either a placebo or Bristol-Myers Squibb’s Tequin, or gatifloxacin, for two years. That trial also showed no effect.

“From a practical point of view, there just isn’t a reason to recommend antibiotic treatment,” said Thomas Grayston, an epidemiologist at the University of Washington and a coauthor of the azithromycin study.

Christopher Cannon, a cardiologist at Brigham & Women’s Hospital in Boston and coauthor of the second study, concurred.

“We looked every which way to see if, for some patients, antibiotic treatment would be beneficial, but none of those groups showed an effect,” Cannon said.

The studies appear in The New England Journal of Medicine.

Both researchers said they still believe Chlamydia plays a role in the development of heart disease, but the damage to the blood vessels caused by the bacteria probably begins too early in life for any antibiotic treatment to be practical.

Cannon said once the infection takes hold, white cells, cholesterol and other substances begin accumulating at the damage site and cause the fatty build-up that blocks arteries over the long term.

Giving people strong antibiotics all their lives to offset the risk would be impractical and possibly more problematic, particularly since overuse of antibiotics is believed to be responsible for the appearance of deadly drug-resistant bacteria.—Reuters