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Differential transplacental binding of diazepam: causes and implications
European Journal of Clinical Pharmacology
|January 1, 1983
Summary
Maternal plasma has higher free diazepam (a sedative) than fetal plasma due to elevated non-esterified fatty acids (NEFA). These fatty acids significantly impact diazepam binding, explaining most differences between mother and fetus.
Area of Science:
- Pharmacology
- Biochemistry
- Obstetrics
Background:
- Diazepam is a commonly used sedative with significant protein binding.
- Understanding drug transfer and binding in the maternal-fetal unit is crucial for neonatal safety.
- Previous studies suggest higher diazepam concentrations in neonates compared to mothers at delivery.
Purpose of the Study:
- To investigate the differences in diazepam plasma binding between maternal and fetal plasma at delivery.
- To identify factors contributing to these binding differences, particularly non-esterified fatty acids (NEFA).
Main Methods:
- Analysis of diazepam plasma binding in 17 matched maternal and fetal plasma pairs.
- In vitro dialysis studies to assess diazepam binding.
- Measurement of plasma non-esterified fatty acids (NEFA), albumin, bilirubin, and total protein.
- Regression analysis to determine the contribution of various factors to diazepam binding.
Main Results:
- Maternal plasma exhibited significantly higher free diazepam percentages (3.24%) compared to umbilical venous (1.50%) and arterial (1.24%) plasma.
- Maternal plasma NEFA concentrations were significantly higher (643 microM) than in umbilical venous plasma (211 microM).
- A strong positive correlation (r=0.871) was found between diazepam % free and plasma NEFA concentration.
- NEFA accounted for approximately 76% of the variability in diazepam % free, with albumin, bilirubin, and total protein having minimal impact.
- NEFA markedly perturbed diazepam binding to human serum albumin (HSA), while bilirubin did not.
Conclusions:
- Elevated maternal plasma NEFA concentrations are the primary determinant of increased free diazepam in maternal circulation at delivery.
- Differences in NEFA levels explain the majority of the variability in diazepam binding between mother and fetus.
- These findings highlight the significant role of NEFA in modulating diazepam pharmacokinetics during pregnancy and emphasize potential differences in fetal vs. maternal albumin binding affinities.