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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<0.01) and dicloxacillin (P<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.

An organosilicon compound, 2,6-cis-diphenylhexamethylcyclotetrasiloxane, cyclic 2,6-cis-[(PhMeSiO)2(Me2SiO)2], was shown to be an orally active estrogen in the mature castrate rat; about 1.0 mg/kg is equivalent to 0.005 mg/kg estradiol benzoate used as a maximum stimulatory dose in a uterotropic assay. Cyclic 2,6-cis-[(PhMeSiO)2(Me2SiO)2] is not an antiestrogen.Cyclic 2,6-cis-[(PhMeSiO)2(Me2SiO)2] is an effective oral postcoital antifertility agent when administered at 0.33 mg/kg on days 1-5 of gestation and at 3.0 mg/kg given on day 1 of gestation. The primary effect appeared to be accelerated passage of ova to the uterus and induction of ovum destruction in the oviduct. At the doses used cyclic 2,6-cis-[(PhMeSiO)2-(Me2SiO)2] was similar to diethylstilbestrol in that tubal retention did not occur as shown for estradiol benzoate. Administration of cyclic 2,6-cis-[(PhMeSiO)2(Me2SiO)2] at other times during gestation terminated pregnancy during primitive streak and neurula stages (days 8-11). Gestation was less sensitive to organosiloxane treatment during implantation. Pregnancy was not terminated after day 11. Thus, this purely organosilicon compound represents a new class of moderate estrogens and may be useful in the study of estrogen structure-activity relationships.