Two very large studies have reached the disappointing conclusion that regularly taking antibiotics (search) doesn't prevent heart disease, as some scientists had hoped.

This had been a promising strategy because lots of work has linked a common respiratory germ to heart attacks and clogged arteries. The germ still may help trigger heart disease, but once people have the condition, attacking the bug does not cut their risk of future heart problems, the studies found.

They were published in Thursday's New England Journal of Medicine.

The germ is Chlamydia pneumoniae (search), but other than being in the same family of bacteria, it has no relation to the sexually spread disease chlamydia.

In one study, led by Dr. J. Thomas Grayston of the University of Washington in Seattle, 4,012 people who had already had a heart attack or clogged artery problem were given either azithromycin (search) or a fake drug once a week for a year.

Nearly four years later, the number of heart attacks, deaths, hospitalizations and necessary additional heart procedures was almost identical between the groups.

The other study tested a different and theoretically more powerful drug, gatifloxacin, on people recently hospitalized for a heart problem. Doctors gave 4,162 patients 10 days of either the drug or dummy pills monthly for an average of two years. Again, the results were very similar.

The studies "reinforce the importance of using proven therapies" like cholesterol-lowering statin drugs in such patients, said the researchers, led by Dr. Christopher Cannon of Brigham and Women's Hospital and Harvard Medical School in Boston.

The federal government and Pfizer Inc. funded Grayston's study. Several of the researchers have ties to the company, and one works for Pfizer. Bristol-Myers Squibb and Sankyo funded Cannon's study, and he and other researchers have received research grants from a variety of makers of antibiotics.

Future research should focus on how the germ may cause heart problems, Dr. Jeffrey Anderson of the University of Utah School of Medicine said in an accompanying editorial.