Interdependency of pharmacokinetic parameters: a chicken-and-egg problem? Not!

Pharmacokinetic (PK) software packages are widely used by scientists in different disciplines to estimate PK parameters. However, their use without a clear understanding of physiological parameters affecting the PK parameters and how different PK parameters are related to each other may result in erroneous interpretation of data. Often, mathematical relationships used for the estimation of PK parameters obscure the true physiological relationships among these parameters, prompting a discussion of which parameter came first and giving the appearance of the-chicken-and-the-egg dilemma. In this article, the author attempts to show how different PK parameters are related to physiological parameters and each other by using various scenarios and examples. In particular, the relationship between clearance and the rate of elimination and that among the other major PK parameters are explored. It is concluded that there is no dilemma in interdependency of the PK parameters, and the relationships among the PK parameters and between PK and physiological parameters are clear.