Placental transfer ratios

Also the placenta has a barrier for hydrophilic and very lipophilic compounds, which is comparable to the blood-brain barrier. Correspondingly, quantitative relationships could be derived for the placental transfer ratios TR of various drugs (eq. 170, recalculated) [775]. The diffusion of drugs into milk and prostatic fluid has been reviewed [472, 761]. 

There is placental transfer of vecuronium, but no effects have been detected in the newborn (the feto-maternal concentration ratio is about 10% less than for pancuronium (31). Postpartum, vecuronium has been reported to have an appreciably longer duration of action (SEDA-13, 105) (32,33) when given in a dose of 0.1 mg/kg. 

Rapid placental transfer was reported in goats and mice. In goats, the fetal plasma levels approached 50% of maternal values within 10 min of the mother receiving an intravenous dose, and the fetal/maternal plasma ratio remained at 0.5 for 1 h, whereas ratios in the liver, kidney, heart, and brain all approached 1 and showed a marked effect on fetal heart rate. In pregnant mice, radiolabeled chlorpromazine rapidly crossed the placenta and accumulated in the eyes of both fetuses and mothers. Marked radioactivity remained in tissues of the eye for 5 months after the drug had been eliminated from other tissues. 

In two mothers, the placental transfer at time of birth, and breast milk concentrations after birth, of vigabatrin enantiomers were examined [172]. Both women had measurable concentrations of vigabatrin in the cord and maternal venous blood. The umbilical vein maternal vein concentrations ranged widely from 7% to 139% in the two women, although the ratios were greater for the R enantiomer than for the S enantiomer in both women. In the breast milk, the level of stereoselectivity was similar to that found in cord blood. The milk plasma concentration ratios of the enantiomers were... 

Foetal depression during spinal and epidural obstetric anaesthesia occurs secondary to maternal hypotension or as a result of placental transfer of the local anaesthetic agent (8, 10 -, 13 ). In this respect, bupivacaine was found to have a low foeto-maternal drug concentration ratio (16 -). When caudal anaesthesia is used, direct injection of the local anaesthetic drug into the foetus is possible (13, Other causes... 

---