Concepts and applications of pharmacokinetic parameters: A guide for the classroom

Abstract

Context: Pharmacokinetic studies play a fundamental role in making informed decisions during the drug development stage and fulfilling regulatory agencies' requirements for drug approval. Disposition profiles of plasma drug concentrations over time can be characterized by using non-compartmental analysis, compartmental and physiological-based modeling. These models allow us to determine the pharmacokinetic parameters that best describe the absorption, distribution, metabolism, and excretion (ADME) processes. Aims: To develop a conceptual and practical guide for the classroom on the most relevant pharmacokinetic parameters and their applications. Results: The apparent volume of distribution (Vd), systemic drug clearance (CL), bioavailability (F) and elimination half-life (t1/2) are among the most relevant pharmacokinetic parameters discussed in this article. The Vd describes the relationship at equilibrium between the amount of drug in the body and its plasma concentrations after distribution, used to calculate the initial dose to reach the target drug concentration. The CL describes the relationship between plasma drug concentrations and the rate of elimination from the body, allowing calculation of a maintenance dosing rate to maintain an average target concentration at steady-state. The t1/2 is the time required to halve the plasma drug concentration, whereas F is critical to understand the biological performance of the drug formulation. Conclusions: In this teacher's topic text, we emphasize the importance of these parameters for optimizing strategies of model-informed dose individualization. Indeed, they are crucial for predicting systemic drug exposures and how long the drug will last in the body, as well as time to steady state after multiple-dosing regimens.