Excretion of progesterone metabolites and estriol in faeces from pregnant women during ampicillin administration

Progesterone metabolites and estriol were determined in urine and faeces collected daily from three pregnant women (33–37 weeks) before and during ampicillin administration (2 g/day orally).

Two of the three subjects showed marked changes in their faecal steroid excretion during ampicillin administration: the faecal progesterone-metabolite pattern changed from containing 69–79% unconjugated metabolites and 19–26% glucuronides under control conditions, to high steroid sulphate content (28–44%); the faecal elimination of 3β-hydroxy-5α-pregnan-20-one and 5α-pregnane-3β,20α-diol glucuronide all but ceased; two 16α-hydroxylated progesterone metabolites were detected in significant amounts in faeces during ampicillin administration but not under normal conditions. Steroid sulphate hydrolysis, epimerization of 3α,5αto 3β,5α-steroids and 16α-dehydroxylation are all well known actions of intestinal bacteria on biliary steroids. It thus seems clear that the changes found in the faecal progesterone metabolite pattern are due to the reduction of the intestinal flora by ampicillin.

Under control conditions the bulk of the faecal estriol was unconjugated. During ampicillin administration this excretion remained unchanged but in addition large quantities of conjugated estriol appeared in the faeces, apparently as a result of inhibition of bacterial deconjugation.

Ampicillin administration also caused decreased urinary excretion of estriol and pregnanediol glucuronide. It seems likely that these well documented effects of ampicillin on urinary steroid excretion are caused by an interruption of the enterohepatic circulation of steroids which results from the inhibition of intestinal steroid metabolism described above.