WASHINGTON (Reuters) - A new antibiotic works well to reduce the misery of traveler's diarrhea, U.S. researchers reported on Tuesday.

Tests of Optimer Pharmaceuticals drug prulifloxacin show it stopped the cramps and diarrhea of so-called Montezuma's Revenge within about a day.

One benefit of the drug over older antibiotics is that it can be taken just once a day, Dr. Herbert DuPont of the University of Texas and St. Luke's Episcopal Hospital in Houston told a news conference.

It has few side-effects and might even be used to prevent diarrhea, which affects up to 40 percent of the 100 million people who visit Latin America, Africa and Asia from other countries, DuPont said.

"The drug could be used prophylactically and I would anticipate it would be highly efficacious," he said.

DuPont tested travelers returning to the United States from Mexico and Peru. It took about 24 hours to cure those with an identifiable infection, such as E. coli, Salmonella, Campylobacter or Shigella, he told a joint meeting of the American Society for Microbiology and the Infectious Diseases Society of America.

In those who could be tested for infection, 71 percent were well within 48 hours after getting prulifloxacin, compared to 33 percent of those given a placebo pill, he said.

Dr. Sherwood Gorbach of Optimer said the drug is approved to treat urinary tract infection in Italy and Japan.

DuPont noted that several drugs are available to treat traveler's diarrhea, but they either do not affect such a wide range of bacteria, the bacteria has evolved resistance to the drugs, or people do not take the pills properly.

Comparable drugs include ciprofloxacin, doxycyclene and ampicillin, but prulifloxacin only needs to be taken once a day for three days.