Characterization of transplacental transfer of paroxetine in perfused human placenta: development of a pharmacokinetic model to evaluate tapered dosing.

The aim of this study was to determine whether a tapered dosage regimen of paroxetine in pregnant women might be useful to avoid withdrawal syndromes in neonates after delivery. We characterized the transplacental transfer of paroxetine in perfused human placenta, fitting a pharmacokinetic model to the results and applying the model and parameters to evaluate a tapered dosage regimen. Paroxetine was perfused from the maternal or fetal side of an isolated human placental preparation with various perfusion protocols, and paroxetine concentrations in the effluent and placental tissue were determined. The transplacental pharmacokinetic parameters of paroxetine were estimated by simultaneous fitting of a five-compartment transplacental pharmacokinetic model to the set of paroxetine concentration profiles. The developed model and parameters were used to simulate the maternal and fetal concentrations of paroxetine, and the results were compared with reported data. Paroxetine showed a larger distribution volume in placental tissue and a smaller transplacental transfer as compared with antipyrine, a passive diffusion marker. A five-compartment model could well describe the transplacental transfer of paroxetine and could well simulate the maternal and umbilical venous concentrations of paroxetine at delivery. Transplacental transfer kinetic parameters of paroxetine were estimated by fitting a pharmacokinetic model to perfusion study data. The model and parameters appeared to be suitable for simulation of paroxetine kinetics in fetus. The model was also applicable to design a dosage regimen to avoid an abrupt decrease of paroxetine concentration in fetal plasma.

Quantitative prediction of fetal plasma concentration of fluvoxamine during dosage-tapering to the mother.

INTRODUCTION: Although selective serotonin reuptake inhibitors have been used during pregnancy for the treatment of depression and anxiety disorders, the fetal plasma concentration profiles of them remained unclear. Therefore, the aim of this study was to develop a pharmacokinetic model to estimate fetal plasma concentration profiles of fluvoxamine, and to clarify the differences with those of paroxetine. METHODS: Perfusion studies using human placentae obtained from full-term pregnant women were conducted to estimate transplacental pharmacokinetic parameters for fluvoxamine. The characteristics of placental permeability were compared with those of paroxetine in our previous report. Using a developed model and these parameters, fetal plasma concentration profiles of fluvoxamine administered to mothers were simulated. RESULTS: The results of perfusion studies and transplacental transfer kinetic parameters indicated that fluvoxamine is less efficiently distributed to placental tissue than paroxetine. The model predicted a maternal-fetal plasma concentration ratio of 0.376 after repeated maternal administration of fluvoxamine, similar to the ratio for paroxetine. However, if the mother ceased taking drug, the model predicted a half-life of fluvoxamine in fetal plasma of 35 h, which is longer than that of paroxetine (10 h). We used the model to evaluate a proposed taper regimen for full-term pregnant women taking fluvoxamine that would minimize the risk of neonatal withdrawal syndrome. DISCUSSION: The obtained parameters and developed model enabled us to predict the fetal plasma concentration profiles of fluvoxamine. The risk of neonatal withdrawal syndrome due to abrupt discontinuation may be less with fluvoxamine than with paroxetine.