Norfloxacin versus placebo for prophylaxis against travellers' diarrhoea.

In a randomized, double blind study, 127 subjects travelling to countries outside Northern Europe were given norfloxacin 200 mg or placebo bid as prophylaxis against diarrhoea. Fifty-six subjects randomized to norfloxacin and 59 to placebo fulfilled criteria for evaluation of efficacy and of those, respectively six and 20 (P = 0.0006) developed diarrhoea. The mean duration of symptoms in the placebo group was 3.6 days, while all subjects on norfloxacin had symptoms for one day only. In travellers to Mediterranean Europe or the Canary Islands, no significant differences were seen between norfloxacin and placebo. Among subjects going to Africa, Asia or Latin America, 4/32 subjects on norfloxacin and 16/30 on placebo developed diarrhoea (P = 0.0004). Adverse effects were few and mild. Faeces for aerobic cultures was obtained before travelling and three weeks and then three months post-treatment. Treatment with norfloxacin resulted in a significant reduction of samples yielding aerobic Gram-negative rods but did not affect enterococci. In the placebo group, Gram-negative organisms other than Escherichia coli were increased on return to Sweden and the subjects frequently acquired Gram-negative organisms resistant to antibiotics. In none of the groups was there a tendency towards increased norfloxacin resistance. Biotyping of E. coli showed that in both groups the subjects changed their E. coli strains frequently during and after travelling. This trial showed that norfloxacin is a safe and effective prophylactic agent with no adverse effect on bacterial flora, but that its use should be restricted to travellers to non-European countries.