Background. Because bacterial pathogens are the primary cause of travelers' diarrhea (TD), antibiotic prophylaxis is effective in TD prevention. This study assessed the efficacy and safety of the nonsystemic antibiotic rifaximin in preventing TD in US travelers to Mexico.

Methods. Healthy adult students traveling to Mexico received rifaximin 600 mg/d or placebo for 14 days and were followed for 7 days post-treatment. Stool pattern and gastrointestinal symptoms were recorded in daily diary entries. The primary end point was prevention of TD during 14 days of treatment measured by time to first unformed stool.

Results. A total of 210 individuals received rifaximin (n = 106) or placebo (n = 104) and were included in the safety population. Median age was 21 years (range, 18–75 y), and the majority of participants were female (65%). Efficacy analyses were conducted in a modified intent-to-treat population of 201 patients who received rifaximin (n = 99) or placebo (n = 102). Rifaximin prophylaxis reduced risk of developing TD versus placebo (p < 0.0001). A smaller percentage of individuals who received rifaximin versus placebo developed all-cause TD (20% vs 48%, respectively; p < 0.0001) or TD requiring antibiotic therapy (14% vs 32%, respectively; p = 0.003). More individuals in the rifaximin group (76%) completed treatment without developing TD versus those in the placebo group (51%; p = 0.0004). Rifaximin provided a 58% protection rate against TD and was associated with fewer adverse events than placebo.

Conclusions. Prophylactic treatment with rifaximin 600 mg/d for 14 days safely and effectively reduced the risk of developing TD in US travelers to Mexico. Rifaximin chemoprevention should be considered for TD in appropriate individuals traveling to high-risk regions.