Faecal level of urobilinogen: an indication for the risk of superinfection and of failure of oral anticonception?

The influence of clindamycin, dicloxacillin, minocycline and norfloxacin on the faecal concentration of urobilinogen was investigated. The studied drugs were administered orally in standard dosage for six days to groups of six volunteers. A decrease in faecal concentration of urobilinogen following administration of clindamycin (P less than 0.01) and dicloxacillin (P less than 0.05) was found. The possible predictive value of a decrease of the faecal level of urobilinogen as an indicator for the impairment of microbial colonization resistance and for the risk of failure of oral anticonceptive treatment is discussed. It is suggested that clindamycin and dicloxacillin should not be combined with oral anticonceptive treatment unless more specific investigations have excluded interaction of these drugs with the oestrogen metabolism in the bowel.