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Pharmacokinetics of Fentanyl in Pregnant Women versus Non-Pregnant Women
Abstract Number: TW-3
Abstract Type: Original Research
Introduction: Physiological changes during pregnancy impact pharmacokinetic parameters of many drugs, including fentanyl. These changes may affect the pharmacodynamics and efficacy of fentanyl administered to laboring women. High-resolution pharmacokinetic studies require frequent blood sampling and are impractical to study in pregnant or laboring patient. The aim of this pilot study was to apply a sparse-sampling technique to examine the effect of term pregnancy on the pharmacokinetics of fentanyl.
Methods: This prospective case-matched study enrolled 15 pregnant and 15 non-pregnant women (total of 30 subjects). The study was approved by the committee on human subjects research prior to enrollment. We planned to obtain two blood specimens from each enrolled women after a 1.5 mcg/kg dose of intravenous fentanyl (based on ideal body weight). The two sampling time points per subject were selected randomly within the following time frames: 0-22 min (first sample) and 23-45 min (second sample). These time frames were based on an optimal sampling time-point schedule if a high resolution pharmacokinetic study were to be performed. Fentanyl plasma concentration results were analyzed using a compartment modeling approach using Phoenix NLME 1.0 (Pharsight, Certara Co.). Pregnancy was coded as a categorical covariate and weight was considered a continuous covariate.
Results: There was no significant difference between the groups in age, height or weight. The fentanyl data was fit to a 1 and 2-compartment model and the 1-compartment model was found to have a superior fit to the data (p<0.001). Fentanyl concentrations over time data are shown in the Figure. The effect of pregnancy and weight did not produce a significant improvement in the model.
Conclusion: In a pilot study of 30 subjects, we found no significant difference in the pharmacokinetics of fentanyl between pregnant and non-pregnant subjects. Findings from this study will be used to further refine this random sparse-sampling technique, a methodology that has great potential utility in studying the pharmacokinetics and pharmocodynamics of drugs in the obstetric population.