Prophylactic Doxycycline for Travelers’ Diarrhea: Results of a Prospective Double-Blind Study of Peace Corps Volunteers in Kenya

We performed a randomized double-blind study to determine the efficacy of doxycycline (100 mg daily) in preventing travelers’ diarrhea among 39 Peace Corps volunteers during their first five weeks in Kenya. The volunteers took either doxycycline or placebo for three weeks and were observed for an additional two weeks. Nine of 21 taking placebo and one of 18 taking doxycycline had travelers’ diarrhea during the treatment period (P = 0.012). The protection seemed to persist for at least one week after the drug was stopped. Enterotoxigenic Escherichia coli was the only pathogen isolated from the placebo group, but was not detected in persons taking doxycycline. None of these organisms were resistant to doxycycline or tetracycline, whereas resistance to tetracyclines and other antibiotics was common among the nonenterotoxigenic Esch. coli. We conclude that doxycycline effectively prevented most episodes of travelers’ diarrhea. (N Engl J Med 298:758–763, 1978) TRAVELERS’ diarrhea, often thought to be one of the unavoidable risks of travel to developing countries, is a syndrome of acute watery diarrhea resulting from infection with one of a variety of enteropathogens, the most common of which are the enterotoxigenic Escherichia coli.^{1 2 3 4} During a previous study in 1975, we found that this syndrome affected 27 of 39 Peace Corps volunteers within the first five weeks of their arrival in Kenya.⁵ The predominant pathogens as in Mexico³⁴ were enterotoxigenic Esch. coli. Furthermore, we found that antibiotic resistance was distinctly unusual among enterotoxigenic Esch. coli in Kenya (88 per cent were.