Understanding the Hysteresis Loop Conundrum in Pharmacokinetic / Pharmacodynamic Relationships


  • Christopher Louizos University of Manitoba
  • Jaime A Yáñez Alcon Research, Ltd., a Novartis Company
  • M Laird Forrest University of Kansas
  • Neal M Davies University of Manitoba




Hysteresis loops are phenomena that sometimes are encountered in the analysis of pharmacokinetic and pharmacodynamic relationships spanning from pre-clinical to clinical studies. When hysteresis occurs it provides insight into the complexity of drug action and disposition that can be encountered. Hysteresis loops suggest that the relationship between drug concentration and the effect being measured is not a simple direct relationship, but may have an inherent time delay and disequilibrium, which may be the result of metabolites, the consequence of changes in pharmacodynamics or the use of a non-specific assay or may involve an indirect relationship. Counter-clockwise hysteresis has been generally defined as the process in which effect can increase with time for a given drug concentration, while in the case of clockwise hysteresis the measured effect decreases with time for a given drug concentration. Hysteresis loops can occur as a consequence of a number of different pharmacokinetic and pharmacodynamic mechanisms including tolerance, distributional delay, feedback regulation, input and output rate changes, agonistic or antagonistic active metabolites, uptake into active site, slow receptor kinetics, delayed or modified activity, time-dependent protein binding and the use of racemic drugs among other factors. In this review, each of these various causes of hysteresis loops are discussed, with incorporation of relevant examples of drugs demonstrating these relationships for illustrative purposes. Furthermore, the effect that pharmaceutical formulation has on the occurrence and potential change in direction of the hysteresis loop, and the major pharmacokinetic / pharmacodynamic modeling approaches utilized to collapse and model hysteresis are detailed.


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Author Biographies

Christopher Louizos, University of Manitoba

Faculty of Pharmacy, Pharmacy Practice Instructor

Jaime A Yáñez, Alcon Research, Ltd., a Novartis Company

Ocular Pharmacokinetics and Disposition, Senior DMPK Study Director

M Laird Forrest, University of Kansas

School of Pharmacy, Department of Pharmaceutical Chemistry

Neal M Davies, University of Manitoba

Faculty of Pharmacy, Dean and Professor




How to Cite

Louizos, C., Yáñez, J. A., Forrest, M. L., & Davies, N. M. (2014). Understanding the Hysteresis Loop Conundrum in Pharmacokinetic / Pharmacodynamic Relationships. Journal of Pharmacy & Pharmaceutical Sciences, 17(1), 34–91. https://doi.org/10.18433/J3GP53



Pharmaceutical Sciences; Review Articles