Effect of ampicillin administration on the excretion of twelve oestrogens in pregnancy urine.

The excretion of twelve oestrogens in urine, pooled daily from a group of pregnant women, was determined before, during and after ampicillin administration (2 g/day, for 3 days). On the second day of ampicillin administration total oestrogen excretion fell to 67% of the mean control value, oestriol excretion to 69% and that of the other eleven individual oestrogens to an average of 62% of the mean control values. In general, on the third day of treatment and on the two post-treatment days this decrease tended to be corrected. The patterns of change in the urinary levels of the individual metabolites provided no clear lead to the basic mechanism of ampicillin impairment of oestrogen excretion. However, as the drug affected all their excretion in more or less the same way as it did that of oestriol, it is possible that ampicillin interferes primarily with their enterohepatic circulation in the mother as has been established with reasonable certainty in the case of oestriol.