Antimicrobial prophylaxis of travellers' diarrhoea: a summary of studies using doxycycline or trimethoprim and sulphamethoxazole.

Antimicrobial therapy of travellers' diarrhoea with doxycycline or a combination of trimethoprim and sulphamethoxazole is effective only while the drugs are being taken. There is no evidence that sub-clinical infections or exposures leads to the development of immunity while the drugs are being taken. When the drugs are withdrawn, an increase in diarrhoea attack rate occurs in those persons who were previously taking the drug. Therefore, the drugs are only effective for short-term use and would not be indicated in persons travelling for long periods of time. Both drugs can be taken once a day, and are therefore convenient to use. There are adverse side effects with these drugs: the possibility of developing a skin rash with TMP-SMX or a photosensitivity reaction with doxycycline must be balanced against the protection afforded. Although both drugs have an effect on normal enteric flora there is no evidence to suggest that this renders the individual more susceptible to other enteric pathogens.