Kinetic-effect models and their applications

Methodological issues in pharmacokinetic-pharmacodynamic modelling

This article presents the theoretical and practical aspects involved in the design and analysis of pharmacokinetic-pharmacodynamic modelling studies. The main features of the protocol of pharmacokinetic-pharmacodynamic studies are discussed with special focus on experimental designs in relation to individual and population approaches. Some basic pharmacodynamic models (such as linear, log-linear, hyperbolic and sigmoid models) are presented as well as more complex time-dependent models (effect compartment and physiological indirect response, tolerance models) which are required when the concentration-effect relationship shows a hysteresis loop. The methods of estimation, with special focus on the individual and populations approaches, are covered, along with the way pharmacodynamic models and methods of estimation can be applied to real data and the information required to criticise the results of modelling. We also present some real problems frequently encountered when performing pharmacokinetic-pharmacodynamic modelling and give some potential solutions (problems with hysteresis loops, lack of convergence, problems with residuals). The last section discusses the significance of pharmacodynamic parameters.

Pharmacokinetic-pharmacodynamic relationships in phase I/phase II of drug development

Early investigation of pharmacokinetic-pharmacodynamic relationships in Phase I/II may facilitate the further clinical development of a new drug. Although some pharmacology assessments in Phase I are often only surrogates for the therapeutic effect, PK-PD modelling of those effects provides in general crucial information on the drug's potency in vivo. A mathematical PK-PD expression allows explorative simulations on the rate of onset of drug action, on the intensity and duration of the effects for doses in future clinical trials, or in situations of altered drug kinetics. Furthermore, understanding of the PK-PD relationship early on in drug development may anticipate unnecessary exposure of human subjects to inappropriate drug doses or trials.

The place of simultaneous pharmacokinetic pharmacodynamic modeling in new drug development: trends and perspectives

The potential applications in drug development of pharmacokinetic-pharmacodynamic modeling are numerous: optimal medication regimen, design of galenic forms, identification of specific effects of metabolites and enantiomers. Nevertheless, this methodology is presently under-used, as appears from an analysis of the literature. We examine this point as well as progress in both non-invasive pharmacodynamic measurement and specific experimental design that could lead to a future extension of PK-PD in toxicology and phase I drug development.