Pharmacodynamic

What is Pharmacodynamic? 

Pharmacodynamics is the study of the biochemical and physiological effects of drugs and their mechanisms of action, as well as the relationships between drug concentration and effect. In other words, it's the study of how drugs interact with the body and how the body responds to those drugs.

Pharmacodynamic effects can include changes in heart rate, blood pressure, respiration, and other physiological responses, as well as changes in behavior and cognition. The study of pharmacodynamics helps to explain why certain drugs are effective for certain conditions and why some drugs have different effects at different doses. It also helps to determine safe and effective dosing regimens for drugs.

Pharmacodynamics Include:

1. Target interaction
2. Mechanism of action. 
3. Pharmacological action.  

Basic type of drug Actions

Drugs not produces a new function but alter the pace of ongoing biological activity either:

1. Stimulation : use for enhancement of cell activity e.g. adrenaline stimulate heart.
2. Depression: use for reducing activity of cell e.g. diazepam depress CNS.
3. Replacement : use for deficiency state e.g. insulin for diabetes.
4. Cytotoxic action: use for selective toxic action on  invading organism or cancer cell without affecting normal host cell e.g. antimicrobial & anticancer.

Drug targets

A drug target is a specific molecule or cellular component that a drug interacts with in order to produce its therapeutic effect.

Drug targets can be classified into several categories, including:

Receptors: Receptors are proteins on the surface of cells or within the cell that bind to specific signaling molecules, such as hormones, neurotransmitters, and cytokines. Drugs can bind to receptors and alter their function, either by activating or blocking them.

Enzymes: Enzymes are proteins that catalyze chemical reactions in the body. Drugs can bind to enzymes and either inhibit or stimulate their activity, leading to changes in metabolic pathways.

Transport proteins: Transport proteins are proteins that help to move substances, such as drugs, across cell membranes. Drugs can bind to transport proteins and either inhibit or enhance their function, affecting the uptake or elimination of drugs from the body.

Nucleic acids: Nucleic acids, such as DNA and RNA, are the building blocks of genetic material. Drugs can bind to nucleic acids and alter their function, leading to changes in gene expression and cellular behavior.

Structural proteins: Structural proteins are proteins that provide structure and support to cells and tissues. Drugs can bind to structural proteins and alter their function, leading to changes in cellular behavior and tissue function.

Protein targets Either :

1. Structural protein like tubulin which is a target for some anticancer (tubulin is a building unit of microtubule involve in cell division)

2. Regulatory protein which include:

• Ion channels.
• Enzymes.
• Carriers or transporters.
• Receptors.

Note: Binding of drug to plasma protein not produce any biological effect and its not apart from pharmacodynamics.

3. Ion channels

There are 3 main type of ion channels depending on gating mechanism:

1. Voltage gated like sodium and potassium channels.
2. Ligand gated ( ligand is any molecule which attaches selectively to particular receptors or sites) 
3. Signal gated.

The drugs interact with channels as:

1. Modulators which enhance channel opening.
2. Blocker which block the channels pore.
3. Opener which open the channels.

The drugs interact withEnzymes and Transporters :

1. Inhibitor:

• Competitive with substrate at catalytic site.
• Non competitive at other site.

2. False substrate.

Drug Receptors

Receptors are proteins found on the surface of cells or within the cell that bind to specific signaling molecules, such as hormones, neurotransmitters, and cytokines.

Receptors play a critical role in transmitting signals between cells and within the body. When a signaling molecule binds to a receptor, it can activate or inhibit the receptor, leading to changes in cellular behavior and physiological responses.

Receptors family 

Receptors can be classified into several families based on their structure, function, and signaling mechanisms. Some of the major receptor families include:

G protein-coupled receptors (GPCRs): This is the largest family of receptors, with over 800 members. GPCRs are involved in a wide range of physiological processes, including neurotransmission, hormone signaling, and sensory perception. They activate or inhibit intracellular signaling pathways through interactions with G proteins.

Ion channel receptors: Ion channel receptors are receptors that are permeable to ions, such as sodium, potassium, and calcium. When these receptors are activated, they can open or close ion channels, leading to changes in electrical signaling in cells. Examples of ion channel receptors include nicotinic acetylcholine receptors, GABAA receptors, and voltage-gated ion channels.

Enzyme-linked receptors: Enzyme-linked receptors are receptors that are linked to intracellular enzymes, such as tyrosine kinases. When these receptors are activated, they can activate or inhibit the associated enzymes, leading to changes in cellular signaling pathways. Examples of enzyme-linked receptors include the insulin receptor, the epidermal growth factor receptor, and the platelet-derived growth factor receptor.

Nuclear receptors: Nuclear receptors are receptors that are located within the nucleus of a cell and regulate gene expression. When these receptors are activated, they can bind to specific DNA sequences and regulate the expression of genes. Examples of nuclear receptors include the steroid hormone receptors, the thyroid hormone receptors, and the retinoic acid receptors.

Immune system receptors: Immune system receptors are receptors that are involved in the recognition and response to foreign substances, such as bacteria, viruses, and other pathogens. Examples of immune system receptors include the T cell receptor, the B cell receptor, and the major histocompatibility complex (MHC) molecules.