Pharmacodynamics Flashcards
Pharmacodynamics
The effect a drug has on the body
Physiological communication of medications
- Stimulus
- First messenger NT/Hormone
- Target receptors within cells
- Intracellular secondary messenger
- Response
where do drug actions take part
- Ion channels
- Receptors
- Enzymes
- Transport proteins
Ion channels as drug targets
Ion channel blockade or opening is useful in controlling functions of cells such as muscles or nerves.
e.g. Sodium entry into the cell excites it leading to contraction in mus
What is lignocaine
Blocks sodium entering the cell and reduces muscle excitability (heart) and stops nerves conducting (central and peripheral nervous system)
Transport Proteins as drugs
Some inhibit transport proteins. Some examples can Ion transport pumps, diuretics, digoxin and selective serotonin reupatke inhibitor
Others drugs use transport proteins as carriers:
L-Dopa (Parkinson’s disease medication) is transported into the body and brain by the large neutral amino acid (LNAA) transporter.
What are receptors
Specefic proteins capable of binding a specific group of drugs or endogenous substances.
Receptors can be :
1. Extracellular- bind neurotransmitters
2. Intracellular- Bind steroids
Ligand
A substance that binds to a receptor.
Can be found in the body(endogenous) or enter the body (exogenous) to bind with a receptor.
Drugs are exogenous ligands as they come from outside the body
e.g. histamine is a ligand at histamine receptors
Effect of Aldosterone
- Aldosterone binds to an intracellular receptor called mineralocorticoid receptor
- Allows nucleus to produce more proteins
- These allow it to regulate the levels of Sodium in the adrenal gland
Receptor theory
- Receptors bind ligands by weak bonds
- Characteristics of shapes and charge give rise to concept of affinity
- Affinity- How well it binds to the receptor
Agonists
- drugs with high affinity and high intrinsic activity.
- Mimic the effect of natural ligand
Antagonists
- drugs with high affinity but no intrinsic activity
- Binding of the drug to the receptor results in no effect
- (receptor is inhibited)
Kinds of Antagonisms
Competitive Antagonists
Non-Competitive Antagonists
Partial Agonists
Competitive antagonists
these compete for the same receptor as an agonist
Non-competitive antagonist
these drugs bind to a place other than the endogenous ligand binding site and incapacitate the receptor.
Partial Agonists
These act on a receptor but without the maximum effect
Classification of receptors
- Receptors are classified by their structure or which ligand binds to them.
- Receptors are subdivided into subtypes
- Subtypes bind similar ligands but generate different effects
- Example, beta receptors
- beta1 in the heart
- beta2 in the lungs
- Example, beta receptors
Drug Selectivity
Drugs may have more than one effect. This is because the same drug may bind to different receptors therefore resulting in a multitude of effects
Drug Potency Vs Efficacy
Potency- strength of the drug/amount of the drug needed to ilicit a certain effect
Efficacy is the maximal possible effect of drug . (Depends on receptor affinity and number)
Look at PPT to understand this
Receptor Down Regulation
- If Drug is agonistic then receptor down regulation may occur
- Body perceives potential for too much effect as too many ligands
- So receptors on membrane reduce for ligand binding
- Less effect (may or may not be right :) )
Consequences
If drug stopped suddenly the body is “starved” of ligand effect, this may give rise to withdrawal or a crisis effect in the body
Receptor Up Regulation
- If the receptor-drug effect is antagonistic then receptor up regulation may occur.
- Body think the effect is too little
- Increase in receptors available for ligand binding
Consequences
overt effect of that ligand in the body, which may be harmful and sometimes fatal.
