Doxycycline prophylaxis of travelers' diarrhea in Honduras, an area where resistance to doxycycline is common among enterotoxigenic Escherichia coli

Daily doxycycline (DX), known to be effective prophylaxis against travelers' diarrhea (TD) in areas of the world where enterotoxigenic Escherichia coli (ETEC) are sensitive to the drug, has not been extensively studied in geographic areas where antibiotic resistance is common. Therefore we studied 44 U.S. Peace Corps Volunteers during their first 5 weeks in Honduras, which is such an area. During the first 3 weeks, volunteers took daily either 100 mg DX or placebo (PL) in a double-blind, randomized fashion. All 22 taking PL developed TD during the first 3 weeks, compared to 7 of 22 (32%) taking DX (P < 0.001); 68% protection). ETEC were isolated from 39% of episodes of TD. From the PL group, ETEC from 7 of 13 stool samples (54%) were resistant to DX, whereas from the DX group. ETEC from 10 of 11 stool samples were resistant (P < 0.05). TD that developed in persons taking DX was also found to be less severe, as judged by length of illness (P < 0.01) and frequency of stools (P < 0.05). This study demonstrates that DX 1) significantly prevents TD even in areas where antibiotic resistance is common, although it does not prevent TD caused by docycycline-resistant ETEC, and 2) significantly diminishes the severity of illness.