Abstract
Cephradine has been described as one of the antimicrobials that do not impair microbial colonisation resistance. However, this view was based on data obtained in animals, and has not been proven in man. In this study we investigated the influence of cephradine, 500 mg twice daily, on microbial colonisation resistance in six healthy volunteers. Increase in the faecal concentration of gram-negative bacilli, aerobic gram-positive cocci or yeasts, and increase in secondary colonisation by strains acquired spontaneously or administered deliberately (challenge), were used as indicators for disturbance of the flora that provides colonisation resistance. In two of six volunteers none of these indicators was found to be positive. In the other four volunteers one or more indicators became positive. It is concluded that even this low dosage of cephradine may impair colonisation resistance. Therefore the view that cephradine does not impair colonisation resistance in a dosage of up to 9 g daily is probably incorrect.