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The Difference Between Toxicokinetics and Toxicodynamics

Toxicology is the science that is concerned with examining the detrimental effects which certain elements, or chemicals would have on animals, human beings, and the environment. Toxicokinetics (TK) and toxicodynamics (TD) are the main key concepts of toxicology. TK refers to how a certain toxin enters the body to reach the target organ/tissue [1]. TK also refers to what the body does to the toxin. TD refers to the dynamic interactions between the toxin and the organ/tissue. TD also refers to what the toxin does to the body [2].

What does toxicokinetics mean? Toxicokinetics comes from the Greek words "Toxikon" meaning "poison," and "Kinetikos" meaning "motion". Toxicokinetics indicates how the body metabolizes certain elements then eliminates them and their metabolites. “Toxicokinetics can be divided into four major stages; Absorption, Distribution, Metabolism and Excretion or Elimination (ADME)” [1]. When the toxins are absorbed into the body, they are typically distributed by the bloodstream to the different organs and tissues. Subsequently, toxins are either eliminated or metabolized then eliminated. They can be eliminated through urine or feces. Toxicokinetic studies are essential to be carried out; understanding the toxicokinetic principles of a certain toxin would help confirm exposure to the toxin by determining which biological tests should be performed [3].

What does toxicodynamics mean? Toxicodynamics comes from the Greek words "Toxikon" meaning "poison," and "dynamikos" meaning "power". “Toxicodynamics determines the relationship between the concentration of a toxicant at the site of action and the toxic effect at the level of molecule, cell, tissue, organ or organism” [4]. In other words, toxicodynamics indicates the signs and symptoms which a certain element causes. Toxicodynamic studies are essential to be carried out; understanding the signs and symptoms caused by certain elements would help develop their antidotes.

Can the toxicokinetics and toxicodynamics of a specific element differ from an individual to another? Yes, human behaviors, age, health, sex, nutritional status, and genetic mutations can alter the toxicokinetic profiles [5]. For instance, people who do not wear face masks when they go out will absorb more smog particles than those who wear face masks. Some diets (e.g., drinking grapefruit) also would impact the distribution, metabolism, and elimination of a certain element. Subsequently, variations in toxicokinetics will contribute to variations in toxicodynamics [1].


1. Croom, E. (2016). The Role of Toxicokinetics and Toxicodynamics in Developmental and Translational Toxicology. Molecular and Integrative Toxicology, 45–81.

2. Rajpoot, K., Katare, P., Tekade, M., Sharma, M. C., Polaka, S., Sengupta, P., & Tekade, R. K. (2022). Toxicokinetic and toxicodynamic considerations in Drug Research. Pharmacokinetics and Toxicokinetic Considerations, 751–776.

3. Chasseaud, L. F. (1992). The Importance of Pharmacokinetic/Toxicokinetic and Metabolic Information in Carcinogenicity Study Design. Drug Information Journal, 26(3), 445–455.

4. Dellafiora, L., Dall'Asta, C., & Galaverna, G. (2018). Toxicodynamics of Mycotoxins in the Framework of Food Risk Assessment-An In Silico Perspective. Toxins, 10(2), 52.

5. Robinson, L. (2018). Factors that Modify Toxicity. A Practical Guide to Toxicology and Human Health Risk Assessment, 45–51.



Author: Madonna A. Fekry

Editor: Lauryn Agron

Health scientist: Madonna A. Fekry

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