• Luciana de Barros Duarte, Elaine Cristine Dantas Moisés, Ricardo Carvalho Cavalli, Vera Lúcia Lanchote, Geraldo Duarte, and Sérgio Pereira da Cunha.
• Deparment of Gynecology and Obstetrics, Faculty of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Brazil. lbdmedi@msn.com
• Eur. J. Clin. Pharmacol. 2009 Aug 1; 65 (8): 803-8.

BackgroundFentanyl is used in obstetrical practice to promote analgesia and anesthesia during labor and in cesarean delivery, with rapid and short-term effects.ObjectiveTo determine fentanyl concentrations in maternal plasma, in the placental intervillous space, and in the umbilical artery and vein in term pregnant women.Patients And MethodsTen healthy pregnant women underwent epidural anesthesia with fentanyl plus bupivacaine and lidocaine, and fentanyl concentrations were determined in the various maternal and fetal compartments, including the placental intervillous space, which has not been previously studied in the literature.ResultsThe ratios of fentanyl concentrations in the various maternal and fetal compartments revealed an 86% rate of placental fentanyl transfer. The highest fentanyl concentrations were detected in the placental intervillous space, being 2.19 times higher than in maternal plasma, 2.8 times higher than in the umbilical vein and 3.6 times higher than in the umbilical artery, with no significant differences between the umbilical vein and artery, demonstrating that there was no drug uptake by fetal tissues nor metabolism of the drug by the fetus despite the high rates of placental transfer.ConclusionThe present study demonstrated that the placental intervillous space acted as a site of fentanyl deposit, a fact that may be explained by two hypotheses: (1) the blood collected from the placental intervillous space is arterial and, according to some investigators, the arterial plasma concentrations of the drugs administered to patients undergoing epidural anesthesia are higher than the venous concentrations, and (2) a possible role of P-glycoprotein (P-gp).

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