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The impact of arteriovenous concentration differences on pharmacodynamic parameter estimates
1Leiden/Amsterdam Center for Drug Research, Division of Pharmacology, The Netherlands.
Journal of Pharmacokinetics and Biopharmaceutics
|February 1, 1997
Summary
Traditional pharmacodynamic (PD) models can overestimate drug effects when using venous concentrations. An extended model accounting for arterial-venous differences improves accuracy, especially when drug elimination is slow or equilibration is delayed.
Area of Science:
- Pharmacology
- Pharmacokinetics
- Mathematical Modeling
Background:
- Pharmacodynamic (PD) investigations often use venous drug concentrations linked to effect-site concentrations via a traditional first-order effect-compartment model.
- This approach overlooks the physiological reality that arterial blood supplies both venous sampling and effect sites.
- An extended effect-compartment model has been proposed to better reflect physiology, incorporating rate constants for arterial-effect site (ke0) and arterial-venous (kv0) equilibrium.
Purpose of the Study:
- To evaluate the bias in PD parameter estimates when using a traditional effect-compartment model with venous concentrations.
- To present an analytical solution for the extended effect-compartment model.
- To assess the performance of the extended model in estimating PD parameters from venous concentrations.
Main Methods:
- Simulated time profiles of venous drug concentrations and drug effect under various values of ke0, kv0, and drug elimination half-life (T1/2).
- Evaluated bias in PD parameter estimates using both traditional and extended effect-compartment models.
- Analyzed conditions under which arteriovenous equilibrium delay impacts PD parameter estimation.
Main Results:
- Significant bias (up to 90%) in PD parameter estimates was observed with the traditional model under specific conditions of T1/2,e0, T1/2,v0, and T1/2.
- Model misspecification in the traditional approach was not evident from fitting results.
- The extended effect-compartment model yielded unbiased but less precise PD parameter estimates.
- The extended model successfully analyzed scenarios with slower venous equilibration and observed proteresis.
Conclusions:
- The traditional model is adequate when T1/2 > 5*T1/2,e0 and T1/2,e0 > T1/2,v0, yielding <10% bias.
- When T1/2 < 5*T1/2,e0 or T1/2,v0 > T1/2,e0, the extended model is necessary for unbiased PD parameter estimation.
- Measuring arterial concentrations is optimal for accounting for arteriovenous equilibration delay; the extended model is a viable alternative if arterial sampling is not feasible, though it requires extensive data.