"Our findings show that rifaximin is an ideal drug for prevention of travelers' diarrhea, an illness that affects an estimated 20 million international travelers each year," said lead author Herbert DuPont, M.D., director of the Center for Infectious Diseases at the University of Texas School of Public Health at Houston and chief of internal medicine at St. Luke's Episcopal Hospital.
"This medication's effectiveness, lack of side effects, and its ability to avoid development of resistant strains of bacteria will allow us to change the way we manage this disease," DuPont said.
The clinical trial reported this week followed 210 U.S. students studying Spanish in Mexico during the summer of 2003. Only 14.74 percent of those who took a daily dose of rifaximin for two weeks suffered from diarrhea, while 53.7 percent of those who took placebos came down with the illness, which also includes nausea, vomiting and stomach pain.
Traveler's diarrhea has been treated for years by antibiotics because it is caused by bacteria found mainly in local food. DuPont's group previously showed that rifaximin is safe and effective therapy for the illness in studies carried out in Mexico, Peru, India and Kenya. The antibiotic has been available in Europe and elsewhere for years to treat diarrhea. The U.S. Food and Drug Administration approved the antibiotic for treatment of traveler's diarrhea a year ago.
But would the treatment also prevent the whole unpleasant experience? And, importantly, would it do so without provoking development of a drug-resistant response by the targeted bacteria?
This last point is crucial, DuPont said, because using other antibiotics such as Cipro as a broad preventive measure would hasten development of bacterial resistance, reducing the future value of the antibiotic to treat pneumonia and other life-threatening diseases.
Lab analysis in the study showed rifaximin did not stimulate resistance in the Escherichia coli (E. coli) bacteria that causes the illness in Mexico, a finding consistent with earlier studies. Unlike other antibiotics, which are absorbed and dispersed throughout the body, research has found rifaximin lingers almost exclusively in the gastrointestinal tract, limiting its ability to stimulate resistance.
Researchers are following up with studies of the drug in Asia, where traveler's diarrhea is caused by other bacteria, such as Shigella, Salmonella and Campylobacter.
And they are following up an earlier finding that 10 percent of those who get traveler's diarrhea develop the more serious irritable bowel syndrome. "If it is found that this drug prevents irritable bowel syndrome, then rifaximin prevention of travelers' diarrhea will go from a good idea to a critical health safeguard," DuPont said.
Co-authors with DuPont, who is also a clinical professor of infectious diseases at Baylor College of Medicine, are: Zhi-Dong Jiang, Ph.D., assistant professor of infectious diseases in the UT School of Public Health; Pablo Okhuysen, M.D., and Charles Ericsson, M.D., professors of infectious diseases at the UT Medical School at Houston; Francisco Javier de la Cabada, M.D., professor of infectious diseases and internal medicine at the University of Guadalajara: Shi Ke, M.D. assistant professor of experimental diagnostic imaging, UT M. D. Anderson Cancer Center; Margaret DuPont, research associate in infectious diseases, UT Medical School at Houston; Francisco Martinez-Sandoval, M.D., dean of the international program at Universidad de Guadalajara.
The investigator-initiated study, registered with the U.S. FDA, was funded by Salix Pharmaceuticals Inc., which markets rifaximin under the brand name Xifaxan.
Journal
Annals of Internal Medicine