Pharmacology is the science of drug and human body interactions. Within pharmacology, pharmacokinetics and pharmacodynamics are two broad yet crucial divisions for pharmaceutical drug discovery and development. Pharmacokinetics (PK) and pharmacodynamics (PD) help understand the complex biochemical interaction between the chemical composition of a drug product and the human body’s natural response. Hence, PK/PD is vital in determining the efficacy and safety of pharmaceutical products.
Regulatory agencies are primarily responsible for bringing safe and effective drugs to the general public. Hence, they predominantly focus on robust assay development in drug discovery and analysis. Assays such as GC-MS and LC-MS are primary assays used to study drug compounds. Besides, the transition of LC-MS assays to LC-MS/MS systems has been a gift for bioanalytical sciences. Both PK/PD studies provide vital data for the approval of a drug product. However, there are differences between PK/PD analyses. Here we share three significant differences between PK and PD analysis.
PK vs. PD
The primary difference between pharmacokinetics and pharmacodynamics is that PK studies drug movement through the body while PD evaluates the body’s response to the drug product. In simpler terms, PK is what the human body does to the pharmaceutical drug, while PD is what the drug product does to the human body.
Different processes for evaluating PK/PD
Pharmacokinetic models depend on the ADME properties of a drug product. Once a drug enters the body, pharmacokinetics evaluates how the drug is absorbed, distributed, metabolized, and excreted from the body. Whereas pharmacodynamic models are based on the effects of drug products on the body. PD studies drug interaction with tissue receptors present on cell surfaces or intracellular fluids. These drug interactions are of seven main types, including depressing action, stimulating action, stabilizing action, blocking/antagonizing action, direct beneficial chemical reaction, direct harmful chemical reaction, and exchanging/replacing action.
Analysis of dose-response curve
Pharmacokinetic studies help enhance drug efficacy while decreasing potential toxicity. The term kinetic homogeneity characterizes the relation between drug concentration at the receptor site and plasma drug concentration. Changes in plasma drug concentration will reflect similar changes in the tissues and receptor sites. If the plasma drug concentration increases, the drug concentration in tissues will increase proportionally. Vice versa, with a decrease in plasma drug concentration, the concentration of the drug will decrease in tissues as well. This property of kinetic homogeneity is the foundation of pharmacokinetic studies.
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Concerning pharmacodynamic studies, PD assesses the relation between drug concentration and effects. These effects include the time course and intensity of therapeutic and adverse effects. The extent of the drug effect depends on the strength of receptor binding, which is irrespective of where the receptor is in the body. For most drug products, drug concentration at the site of action dictates the effects drugs may have on the body. However, other factors may affect drug intensity. These other aspects include the mechanism of signal transduction, density of cell receptors, and regulatory factors. These diverse factors are why different individuals have different responses to the same drug product.