Difference Between Pharmacokinetics and Pharmacodynamics

The key difference between pharmacokinetics and pharmacodynamics is that pharmacokinetics studies how an organism affects a drug while pharmacodynamics studies how a drug affects an organism.

Pharmacology is the study of interactions between a drug and an organism. Pharmacokinetics and pharmacodynamics are the main components of pharmacology. This shows the interactions between both endogenous and exogenous chemical substances and living organisms. Both pharmacokinetics and pharmacodynamics are a part of large molecule bioanalytical studies. These studies help in the discovery and development of new drugs in the pharmaceutical industry.

CONTENTS

1. Overview and Key Difference
2. What is Pharmacokinetics 
3. What is Pharmacodynamics
4. Similarities – Pharmacokinetics and Pharmacodynamics
5. Pharmacokinetics vs Pharmacodynamics in Tabular Form
6. Summary – Pharmacokinetics vs Pharmacodynamics

What is Pharmacokinetics?

Pharmacokinetics studies how an organism affects a drug. It describes how the body reacts to a specific chemical or xenobiotic after it is administered to an organism. Pharmacokinetics of a drug depends on few factors such as the patient’s age, sex, renal function, genetic makeup as well as chemical properties of the drug. The properties of the pharmacokinetics of chemicals are affected by the administration route and the drug dose. This also affects the absorption rate.

Figure 01: Pharmacokinetics vs Pharmacodynamics

Process of Pharmacokinetics

There is a model to observe the processes which take place in pharmacokinetics. The model is divided into five compartments and referred to as the LADME scheme. LADME refers to liberation, absorption, distribution, metabolism and excretion. Liberation is the release of the drug to produce a final medicinal product. Absorption is the process of the drug or substance entering the blood circulation system. Distribution is the dispersion of the drug or substances throughout the fluids and tissues of the body. Metabolism is the recognition of the foreign substance by the organism and the irreversible transformation of initial compounds to metabolites. Excretion is the removal of substances from the body. Pharmacokinetics analyses are characterized through drug concentration versus time in a dose-response curve.

What is Pharmacodynamics?

Pharmacodynamics is the study of the biochemical and physiological effects of drugs in the body. It shows the interaction of the drug with tissue receptors which are located at the cell membranes or in the intracellular fluid. Pharmacodynamics plays an important role in dose-response relationships. That is the relationship between the drug concentration and effect. There are seven main actions of drugs on how they act on the body. They are the stimulating action, depressing action, blocking/antagonizing action, stabilizing action, exchanging/replacing action, direct beneficial chemical reaction, and direct harmful chemical reaction.

Figure 02: Pharmacodynamics

Both stimulating and depressing actions have direct receptor agonism and downstream effects. During blocking/antagonizing action, the drug binds to the receptor without activating it. During stabilizing action, the drug is neutral. It does not act as a stimulant or a depressant. Exchanging/replacing action helps the drug accumulate to form a reserve. Direct beneficial chemical reaction prevents damages caused by free radicals, while direct harmful chemical reaction results in the destruction of the cells. Pharmacodynamics analyses are characterized through drug effect versus time in the dose-response curve.

What are the Similarities Between Pharmacokinetics and Pharmacodynamics?

• Both pharmacokinetics and pharmacodynamics are about the concentration of a drug in the body.
• Pharmacokinetics and pharmacodynamics analysis play an important role in characterizing drug exposure, predicting drug dosages, estimating the rates of drug elimination and absorption, assessing relative bioequivalence, characterizing variability, establishing safety margins and efficacy characteristics and understanding the concentration-effect relationships.

What is the Difference Between Pharmacokinetics and Pharmacodynamics?

Pharmacokinetics is the movement of drugs throughout the body and how the body affects the drug. Pharmacodynamics is the biological response of the body to the drugs. So, this is the key difference between pharmacokinetics and pharmacodynamics. Moreover, pharmacokinetics shows the exposure of drugs through liberation, absorption, distribution, metabolism ad excretion. Pharmacodynamics shows the response to drugs through biochemical and molecular interactions.

The below infographic lists the differences between pharmacokinetics and pharmacodynamics in tabular form.

Summary – Pharmacokinetics vs Pharmacodynamics

Pharmacology is the study of interactions between a drug and an organism. Pharmacokinetics is the study of how an organism affects a drug. It describes how the body reacts to a specific chemical or xenobiotic after it is administered to an organism. Pharmacodynamics is the study of the biochemical and physiological effects of drugs on the body. It depicts the interaction of the drug with tissue receptors which are located at the cell membranes or in the intracellular fluid. Pharmacokinetics consists of five principles: liberation, absorption, distribution, metabolism and excretion. Pharmacodynamics plays an important role in dose-response relationships. That is the relationship between the drug concentration and effect. The pharmacokinetics analysis (drug concentration versus time) and pharmacodynamics analysis (drug effect versus time) act as important tools in the discovery and development of new drugs. Thus, this summarizes the difference between pharmacokinetics and pharmacodynamics.

Reference:

1. Farinde, Abimbola. “Overview of Pharmacodynamics – Clinical Pharmacology.” MSD Manual Professional Edition.
2. “Pharmacokinetics & Pharmacodynamic (PK/PD) Services.” Nuventra Pharma Sciences.

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