Chapter 4
Pharmacodynamics
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Principles of Drug Action
Drugs are chemical substances that modify biological responses by interacting with macromolecular targets such as receptors, ion channels, transporters, ...
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Targets for Drug Action: Overview
Drugs target macromolecules to modify ongoing cellular processes. Primary drug targets include receptors, ion channels, transporters, and enzymes.
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Signal Transduction: Overview
Cells respond to many types of information, often through receptor proteins positioned on the membrane. They respond to chemical signals, such as ...
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Transducer Mechanism: G Protein–Coupled Receptors
G Protein–Coupled Receptors (GPCRs) are membrane-bound receptors that transiently associate with heterotrimeric G proteins and induce an appropriate ...
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Ligand-Gated Ion Channel Receptor: Gating Mechanism
Ligand-gated ion channels are transmembrane proteins that play a vital role in intercellular communication and functions of the nervous system. They allow ...
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Transducer Mechanism: Enzyme-Linked Receptors
Enzyme-linked receptors are cell-surface receptors acting as an enzyme or associating with an enzyme intracellularly. They make excellent drug targets. ...
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Transducer Mechanism: Nuclear Receptors
Nuclear receptors, or NRs, are unique transcription factors that regulate gene transcription and affect the cellular pathways involved in reproduction, ...
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Dose-Response Relationship: Overview
Agonists can bind with and activate receptors, resulting in the formation of drug-receptor complexes. Once formed, these complexes catalyze many ...
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Dose-Response Relationship: Potency and Efficacy
The potency of a drug is the measure of its ability to produce a biological response and can be compared by looking at the half-maximum effective ...
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Dose-Response Relationship: Selectivity and Specificity
Drugs exert their therapeutic effects by interacting with receptors, enzymes, or ion channels that are present throughout the human body. The strength and ...
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Therapeutic Index
The therapeutic index of a drug is a key parameter in pharmacology that quantifies the relative safety of a drug by calculating the ratio between the dose ...
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Drug-Receptor Interaction: Agonist
Agonists are drugs that interact with specific receptors in the body to produce a biological response. When an agonist binds to a receptor, it activates ...
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Drug-Receptor Interaction: Antagonist
An antagonist is a drug that binds strongly to a receptor without activating it. An antagonist prevents other molecules, such as neurotransmitters or ...
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Combined Effects of Drugs: Antagonism
The combined effects of drugs can result in various interactions, of which an important type is antagonism. Antagonism is a mechanism where one drug ...
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Combined Effects of Drugs: Synergism
Synergism is a useful mechanism where combining two or more drugs is more effective than each constituent used alone. Such combinations are also called ...
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Spare Receptors
Some receptors remain unoccupied even when an agonist produces a maximal response. Such empty ones are called spare receptors. In presence of spare ...
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Quantitative Aspects of Drug-Receptor Interaction
The receptor occupancy theory connects a drug's response to the number of occupied receptors. With higher drug concentrations, more receptors are ...
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The Two-State Receptor Model
The two-state receptor model explains a drug's interaction with receptors, such as G protein-coupled receptors and ligand-gated ion channels, to ...
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Desensitization and Tachyphylaxis
Tachyphylaxis is described as a rapid decrease in response to a drug after repeated or continuous administration of the same drug dose. It is a phenomenon ...
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