Transvaginal absorption and disposition of nonoxynol-9 in gravid rats.

The placental transfer, maternal tissue distribution and elimination of [14C]-nonoxynol-9 (25 mg/kg) were studied during the first 6 h in 15-day pregnant rats treated intravaginally. Blood concentrations of 14C reached a maximum of 2.0 +/- 0.06 micrograms/ml in 1 h, declining slowly in 3 h, and remaining steady thereafter. At 6 h, the highest levels of 14C were recorded in the maternal urinary bladder, followed by those in the liver, kidney, adrenal and thyroid. The maternal brain showed lowest uptake of 14C among all tissues examined. After 6 h, the 14C concentrations in the uterus or placenta were similar to that of maternal plasma, whereas the mean concentrations of 14C both in the amniotic fluid and fetus were approx. one-third of that of the maternal plasma. About 44% of the administered dose was absorbed from the vagina, and nearly 17% of the per vaginum applied radioactivity was recovered in the urine and feces over 6 h. The results show that nonoxynol-9 (N-9) is rapidly absorbed into the blood stream from the vagina of gravid rat and that the fetal uptake of 14C is much lower than that of the placenta.