TRENTON, N.J. (AP) — Could taking an antibiotic spare heart patients from future heart attacks, bypass surgery or even death?

Researchers hope to find out with a federally funded study based on growing evidence a common bacterial infection may trigger heart attacks and worsen, perhaps even cause, atherosclerosis — narrowing of the arteries from plaque deposits.

Given that known risk factors for heart disease such as smoking, high cholesterol and high blood pressure can't account for many cases, doctors increasingly suspect infectious agents may be partly to blame for some of the 1.75 million heart attacks, bypass surgeries and artery-clearing angioplasties in this country each year.

The prime suspect: a bacteria called Chlamydia pneumoniae, a cousin to the sexually transmitted form of Chlamydia that instead causes pneumonia and bronchitis.

"Maybe 60 percent of the population have gotten it in the past," often without becoming ill, said Dr. John Kostis, chairman of medicine at the Robert Wood Johnson Medical School in New Brunswick, one of 26 sites used in the study.

Dr. Jeffrey Anderson, chief of cardiology at the University of Utah Medical Center in Salt Lake City, said that just as doctors have learned many peptic ulcers are caused by a bacterial infection and can be treated with antibiotics, the same could be true with some heart disease cases.

"Antibiotic therapy could become a major breakthrough treatment against a disease that kills more Americans each year than any other disease," he said.

Half of the 4,000 heart disease patients to be studied will be given a weekly antibiotic pill, Zithromax, for one year, while the comparison group gets a dummy pill. Neither will know who is taking which pill.

The two groups will be compared over four years to see which has more heart "events" — deaths, heart attacks, increasing atherosclerosis requiring surgery, and major chest pain, which indicates the heart isn't getting enough oxygenated blood.

Blood from some patients will be tested to see if the antibiotic is killing the bacteria, lead researcher Dr. J. Thomas Grayston, professor of epidemiology at the University of Washington in Seattle, said last week.

Zithromax was chosen because it is long-acting and, unlike most antibiotics, can get inside cells, where the tough-to-kill Chlamydia can hide, dormant, for years, he said.

A recent surge of research generally shows the majority of patients studied who had heart attacks or other complications had been infected by Chlamydia pneumoniae.

"We don't know if it's a cause or an innocent bystander," said Sonia Skarlatos of the National Heart, Lung and Blood Institute, a part of the National Institutes of Health providing $11 million for the project.

Early, small studies have shown that giving Zithromax, known generically as azithromycin, to patients after a heart attack reduces chances of a second one.

Pfizer, the drug's maker, is conducting a similar trial, giving the antibiotic for three months to half of the 3,600 heart attack victims in the study, according to Michael Dunne, director of its central research division in Groton, Conn.

Grayston said comparing results of the three-month and yearlong treatments, and other differences between the two studies, could help in determining which patients might benefit most from preventive antibiotic treatment.

"It's not going to be like immunization for polio, make (heart disease) go away," Kostis said, but it may well help many heart patients.

EDITOR'S NOTE: Heart patients interested in participating in the study should call the coordinating center at 206-577-0259.

Copyright 1999 The Associated Press. All rights reserved.