Chapter 2: Drug Receptors & Pharmacodynamics
Introduction to Pharmacodynamics
Pharmacodynamics is the study of what the drug does to the body. It explains how
drugs produce their effects by interacting with specific targets in the body.
Pharmacodynamics includes the study of:
Drug receptors
Drug–receptor interactions
Mechanisms of drug action
Relationship between drug concentration and response
Therapeutic and adverse effects of drugs
The difference between pharmacodynamics and pharmacokinetics:
Pharmacodynamics (PD):
What the drug does to the body.
Pharmacokinetics (PK):
What the body does to the drug.
Pharmacokinetics involves:
Absorption
Distribution
Metabolism
Excretion
While pharmacodynamics focuses on the effects produced after the drug reaches its
site of action.
Drug Receptors
Most drugs produce their effects by interacting with specific molecules called drug
receptors.
A receptor is usually a protein molecule located:
On the cell membrane
Inside the cytoplasm
Inside the nucleus
The binding of a drug to its receptor initiates a series of events that leads to a
biological response.
,Examples:
A drug binding to receptors in the heart can change heart rate.
A drug binding to receptors in the brain can alter
nervous system activity. Functions of Drug
Receptors
Drug receptors have four major functions
1. Recognition
Receptors are responsible for recognizing specific drugs or endogenous substances.
The interaction between a drug and its receptor depends on the chemical structure of
both molecules.
This specificity is often described by the:
Lock-and-key model
The receptor represents the lock.
The drug represents the key.
Only drugs with the correct structure can bind effectively to a receptor.
2. Signal Transduction
After a drug binds to its receptor, the receptor converts this interaction into an
intracellular signal.
This process may result in:
Activation of enzymes
Opening or closing of ion channels
Production of intracellular signaling molecules
Changes in gene expression
The final result is the pharmacological effect of the drug.
3. Amplification
A small number of drug molecules can produce a large biological response because
receptor activation can amplify signals inside the cell.
, For example:
A small amount of hormone binding to receptors can produce significant changes in
many cells.
4. Regulation of Receptors
Cells can regulate the number and sensitivity of receptors depending on the level of
stimulation.
Up-regulation
Up-regulation occurs when cells increase the number of receptors.
It usually happens when receptors are blocked or when stimulation decreases for a
long period.
Effects:
Increased receptor number
Increased sensitivity to the drug or natural ligand
Down-regulation
Down-regulation occurs when cells decrease the number of receptors.
It usually happens after prolonged exposure to high levels of a drug or agonist.
Effects:
Decreased receptor number
Reduced response to the drug
This process contributes to:
Drug tolerance
where higher doses are required to produce the same effect.
Types of Drug Receptors
There are four major types of drug receptors:
1. Ligand-gated ion channels
2. G protein-coupled receptors (GPCRs)
3. Enzyme-linked receptors
4. Intracellular receptors
Introduction to Pharmacodynamics
Pharmacodynamics is the study of what the drug does to the body. It explains how
drugs produce their effects by interacting with specific targets in the body.
Pharmacodynamics includes the study of:
Drug receptors
Drug–receptor interactions
Mechanisms of drug action
Relationship between drug concentration and response
Therapeutic and adverse effects of drugs
The difference between pharmacodynamics and pharmacokinetics:
Pharmacodynamics (PD):
What the drug does to the body.
Pharmacokinetics (PK):
What the body does to the drug.
Pharmacokinetics involves:
Absorption
Distribution
Metabolism
Excretion
While pharmacodynamics focuses on the effects produced after the drug reaches its
site of action.
Drug Receptors
Most drugs produce their effects by interacting with specific molecules called drug
receptors.
A receptor is usually a protein molecule located:
On the cell membrane
Inside the cytoplasm
Inside the nucleus
The binding of a drug to its receptor initiates a series of events that leads to a
biological response.
,Examples:
A drug binding to receptors in the heart can change heart rate.
A drug binding to receptors in the brain can alter
nervous system activity. Functions of Drug
Receptors
Drug receptors have four major functions
1. Recognition
Receptors are responsible for recognizing specific drugs or endogenous substances.
The interaction between a drug and its receptor depends on the chemical structure of
both molecules.
This specificity is often described by the:
Lock-and-key model
The receptor represents the lock.
The drug represents the key.
Only drugs with the correct structure can bind effectively to a receptor.
2. Signal Transduction
After a drug binds to its receptor, the receptor converts this interaction into an
intracellular signal.
This process may result in:
Activation of enzymes
Opening or closing of ion channels
Production of intracellular signaling molecules
Changes in gene expression
The final result is the pharmacological effect of the drug.
3. Amplification
A small number of drug molecules can produce a large biological response because
receptor activation can amplify signals inside the cell.
, For example:
A small amount of hormone binding to receptors can produce significant changes in
many cells.
4. Regulation of Receptors
Cells can regulate the number and sensitivity of receptors depending on the level of
stimulation.
Up-regulation
Up-regulation occurs when cells increase the number of receptors.
It usually happens when receptors are blocked or when stimulation decreases for a
long period.
Effects:
Increased receptor number
Increased sensitivity to the drug or natural ligand
Down-regulation
Down-regulation occurs when cells decrease the number of receptors.
It usually happens after prolonged exposure to high levels of a drug or agonist.
Effects:
Decreased receptor number
Reduced response to the drug
This process contributes to:
Drug tolerance
where higher doses are required to produce the same effect.
Types of Drug Receptors
There are four major types of drug receptors:
1. Ligand-gated ion channels
2. G protein-coupled receptors (GPCRs)
3. Enzyme-linked receptors
4. Intracellular receptors
