Difference between Pharmacokinetics and Pharmacodynamics!

In the dynamics of pharmacology, the terms pharmacodynamics and pharmacokinetics, often regarded as identical concepts. However, there is a huge different betw

FORENSIC SCIENCEFORENSIC PHARMACOLOGY

Shubham Kumar

1/29/20248 min read

human heart scale model
human heart scale model
person holding brown and black round ornament
person holding brown and black round ornament

In the dynamics of pharmacology, the terms pharmacodynamics and pharmacokinetics, often regarded as identical concepts. However, there is a huge different between them. Furthermore, both the terms determine the behavior of drug when it interact with the living biological system. Therefore, many people are always gets confused about these two terms. If you are also facing the same issue, don't worry we are here to clear your all confusions.

In this post we are going to discover the difference between pharmacodynamics and pharmacokinetics.

Pharmacodynamics

The term pharmacodynamics is originated from the Greek word "pharmakon" meaning "drug" and "dynamikos" meaning "power". Pharmacodynamics refers to the specialized branch of pharmacology which deals withe the study of drug's molecular, biological and psychological actions on the living being. Here living being generally refers to the human beings, however, animals also lands on the same domain as human does.

Pharmacodynamics concentrates to discover the actions of drugs when exposed to the target receptors. Furthermore, analyze whether drug is providing therapeutic effect or harmful effect. Moreover, determining the biological response towards the exposer of a particular drug. The domain of pharmacodynamics, scientists also detects the concentration of active drug required to ensure lower side effects on the biological system.

There are three key concepts in the branch of pharmacodynamics, which regulates the action of drugs on the target receptors. These are regulatory proteins (receptors), affinity and efficacy. Here regulatory protein are the opening gates for the effect of drugs on biological system. These proteins are the enzymes or macromolecules, with which the drugs interact to launch their effect. The strength with which a drug bind with its target is called affinity, while the ability of drug to launch the response, once its attached to its target, is called efficacy.

Sub-domains of Pharmacodynamics | Receptor, Efficacy, Affinity

The terms receptors, efficacy and affinity, are the key concepts in the pharmacodynamics that describes the interaction between drugs and their targeted biological system.

Regulatory Protein | Receptor

The receptors are specific proteins and enzymes located in the biological systems (targets of drugs). When a drug enters into the biological system, it starts its action on the targeted biological system. However, before its action, it first attaches with the receptor protein. Therefore, receptor proteins are the enzymes or macromolecules, with which the drug interact and attach, to produce its effect. There are different types of receptors present throughout the whole body.

  • Cell Surface Receptors: The cells have two types of receptors, G Protein Coupled Receptors (GPCRs) and ion channel receptors. GPCRs is located in the cell membrane, whereas ion channel are located on the cell membrane.

  • Intracellular Receptor: Located within the cell, in cytoplasm and nucleus. It is also called nuclear receptor.

  • Enzyme-Liked Receptor: They are found on the cellular surface and inherit intrinsic enzymatic activity.

  • Neurotransmitters Receptors: These are receptors for the neurotransmitters, present on the synapses between nerve cells.

  • Harmone Receptors: These receptors are for the organs and tissues producing the endocrine hormones.

  • Immune system Receptors: These receptors recognize antigens and hold prominent grounds in immune response. like T-cell receptor and B-cell receptor.

Affinity

Affinity refers to the strength with which the drug is bonded with its targeted receptor. Specifically, it is the degree of how well the drug is attached to its target receptor. The affinity lands a very prominent role in drug response, as an ability to bond properly is the sign of potent drug. Therefore, it can blow a significance response even when present in low concentrations.

Characteristics:

If any drug has high drug affinity, then it means that drug is specialized in having a tight bond with its receptor enzyme.

However, the affinity of the drug is influenced by the chemical structure or drug, consequently the nature of the binding receptor. Therefore, it is important to determine the drug ascertain to the nature of the receptor, as it will automatically increase the drug affinity.

Affinity of a drug is described as equilibrium dissociation constant (kd). The lower the (kd), the higher the drug affinity.

Application:

A drug with the low equilibrium dissociation constant, generally referred to as having high drug affinity, and this a sign of a potent drug. These potent drugs are specialized in providing the significance amount of effect even when present in the low concentration.

Affinity of a drug is required to determine the dosage needed to achieve a therapeutic effect.

Efficacy

Efficacy refers to the ability of a drug to initiate the maximum response when it is bonded with its targeted receptor. Specifically, it is the drug's inherent ability through which it activates the receptor and initiates the maximum response. The efficacy lands a very prominent role in drug response, as an ability to launch the maximum response is the sign of full agonists drug. Moreover, the efficacy is not related to the drug's affinity.

Characteristics:

The drugs who have high efficacy are know for launching the maximum response. This is the maximum and upper limit a system can achieve.

The efficacy of a drug is independent of the drug's affinity. The drug with high affinity may or may not have the high efficacy.

The partial agonists have generally lower efficacy than that of full agonists. This is because, the partial agonists are known for producing the sub maximum response, even when the maximum receptors are attached, whereas full agonists are known for initiating the maximum response, even when they are in low concentration.

Application:

The efficacy determine the maximum amount of a response a drug can elicit. Moreover, determining the intensity of response, which further help to analyze the dosage required to launch therapeutic effect.

Efficacy is majorly preferred to select the drugs to use in medical purposes. The drugs with higher efficacy is majorly preferred in those cases which required robust response.

Pharmacokinetics

The term pharmacokinetics is the specialized branch of pharmacology which encompasses the study of movements of drugs within the body. Pharmacokinetics is concerned with the study of how the body absorbs, absorbs, metabolize, distributes and excrete drugs. It defines the process by which the drug entered into the body, is first gets absorbed by the bloodstreams, then distributed to required tissues and organs within the body by blood streams, then metabolizes into actine and inactive compounds and finally gets excreted.

Pharmacokinetics is often concerned with the determination of time taken by the drug to go through absorption to distribution to metabolism to excretion, usually regarded as ADME process. The process holds prominent grounds in determination of appropriate dosage regimen for a drug. Moreover, taking care of its therapeutic effects, and predicting its potential side effects, when it gets mixed with other substance present within the body.

The study of pharmacokinetics is important so as to analyze about how drugs move within the body. Moreover, holds crucial grounds in optimizing proper drug therapy, maximizing therapeutic effects and ensuring patients safety and efficacy.

ADME Process | Absorption, Distribution, Metabolism and Excretion

The ADME process founds its potential applications in pharmacokinetics so as to track the route of drugs injected in the body, and identifying its potential side effects on each level of its route. The ADME process refers to the Adsorption, Distribution, Metabolism and Excretion of drugs in the body. These fours process holds prominent grounds in determining the concentration of drug required by the body, its therapeutic effects and potential side effects.

Absorption

The first step where the ADME process begins is Absorption. Absorption refers to the process by which the drug enters into the bloodstreams from its site of administration. Moreover, the site of administration depends upon the state or from in which the drug is being taken. Depending on the drug's form (such as oral tablets, injections, or topical creams), absorption can occur through various routes, including oral (through the digestive system), intravenous (directly into the bloodstream), subcutaneous (under the skin), intramuscular (into the muscle), or through the skin.

The properties of administered drug and the membranes within the body, have heavy influence on the absorption if drugs from various route, drugs movements in the bloodstreams and its distribution. Furthermore, the rate and extent of absorption can seemingly affect the drug's bioavailability.

Bioavailability is the sub-part of absorption, which define the actual amount of drug reaches the systematic circulation. In pharmacology, bioavailability is a subcategory of absorption, and is a fraction of an administered drug that reaches the systematic circulation.

The First Pass Metabolism effect (Pre-systematic effect) is a phenomenon of drug metabolism at a specific location in the body, which leads to decrease in concentration of active drug. Specifically, those drugs which are administered orally, before they can reach to site of action, they passes though various membranes and biological system. Furthermore, leading to reduction in concentration of active drug.

Distribution

After absorption, the next step comes is distribution. The term distribution in ADME refers to the process by which the absorbed drug in bloodstreams is distributed to the tissues and organs. In simple terms, a process by which the drug passes from the bloodstream to the tissues and organs. The drugs binds themselves with the proteins in blood and transported to various tissues and organs. Distribution is influenced by factors such as blood flow, tissue permeability, the effect of ph on solubility, partition/distribution coefficients, and the drug's affinity for proteins. The drug moves from intravascular space (bloodstreams) to extravascular space (tissues and organs), the process is carried out in a circulatory system.

The distribution process arose questions in mind that, how drug crosses the biological membrane? The answer is, drugs crosses the biological membrane via simple or passive diffusion. The drug molecules moves across the cell from higher concentration to lower concentration. In this process, cellular diffusion is not required. Passive diffusion is divided into lipid and aqueous diffusion.

Metabolism

Metabolism is the process by which the body chemically alters the drug to make it more water-soluble and easier to excrete. Most drug metabolism occurs in the liver, where enzymes transform drugs into metabolites. These metabolites can be active, inactive, or even toxic. Metabolism helps the body eliminate drugs more efficiently, although in some cases, it can also convert a prodrug (an inactive form of a drug) into its active form.

Excretion

The term excretion in ADME refers to the process by which drug is removed from the body, either as metabolite or unchanged drug. There are various routes of excretion including urine, bile, sweat, saliva, tears, milk, and stool. Although all the routes are essential, however, kidney and livers are most important excretory organs. Furthermore, kidney is responsible for majority of water-soluble excretions. Moreover, the kidneys filter drugs and their metabolites from the bloodstream, and these substances are eventually eliminated from the body.

Understanding the ADME process is essential for drug development, dosing regimens, and predicting drug interactions. It helps healthcare professionals and researchers optimize drug therapies and minimize the risk of adverse reactions in patients.

I hope this post has achieved its aim to provide you information regarding the difference between pharmacodynamic and pharmacokinetics. Stay safe, stay connected to it's forensic.

Reference

  • "Forensic DNA Typing" by John M. Butler

  • "The Forensic Casebook: The Science of Crime Scene Investigation" by Ngaire E. Genge

  • "Forensic Science: A Very Short Introduction" by Jim Fraser

  • "Practical Crime Scene Processing and Investigation" by Ross M. Gardner