Antimicrobial agents in the prevention of travelers' diarrhea.

Each of 433 adults traveling to Guadalajara, Mexico, from the United States during summer months was enrolled in one of four clinical trials of the protective effect of antimicrobial agents against travelers' diarrhea. Only one (2%) of 57 subjects taking trimethoprim-sulfamethoxazole (160 mg/800 mg daily) experienced diarrhea during a two-week study, whereas eight (14%) of 58 subjects taking trimethoprim alone (200 mg daily) and 10 (33%) of 30 taking placebo developed illness (P less than .05 and P less than .0001, respectively). Diarrhea occurred significantly less frequently among subjects receiving trimethoprim than among placebo recipients (P less than .05). None of 11 students given bicozamycin (500 mg four times daily) developed diarrhea during a three-week study, whereas 10 (53%) of 19 placebo recipients became ill (P = .003). Four (7%) of 54 subjects receiving norfloxacin (400 mg daily) experienced diarrhea during a two-week study; in contrast, 34 (60%) of 57 placebo recipients developed diarrhea (P less than .0001). The various antimicrobial agents prevented illness due to enterotoxigenic Escherichia coli and Shigella as well as that unassociated with a pathogen. The drugs were well tolerated. Current evidence suggests that trimethoprim-sulfamethoxazole is the optimal antimicrobial agent available for prophylaxis of travelers' diarrhea.